Index: b/Lib/sysconfig.py
===================================================================
--- a/Lib/sysconfig.py
+++ b/Lib/sysconfig.py
@@ -231,11 +231,19 @@ def _parse_makefile(filename, vars=None)
                     done[n] = v
 
     # do variable interpolation here
-    while notdone:
-        for name in notdone.keys():
+    variables = list(notdone.keys())
+
+    # Variables with a 'PY_' prefix in the makefile. These need to
+    # be made available without that prefix through sysconfig.
+    # Special care is needed to ensure that variable expansion works, even
+    # if the expansion uses the name without a prefix.
+    renamed_variables = ('CFLAGS', 'LDFLAGS', 'CPPFLAGS')
+
+    while len(variables) > 0:
+        for name in tuple(variables):
             value = notdone[name]
             m = _findvar1_rx.search(value) or _findvar2_rx.search(value)
-            if m:
+            if m is not None:
                 n = m.group(1)
                 found = True
                 if n in done:
@@ -246,23 +254,48 @@ def _parse_makefile(filename, vars=None)
                 elif n in os.environ:
                     # do it like make: fall back to environment
                     item = os.environ[n]
+
+                elif n in renamed_variables:
+                    if name.startswith('PY_') and name[3:] in renamed_variables:
+                        item = ""
+
+                    elif 'PY_' + n in notdone:
+                        found = False
+
+                    else:
+                        item = str(done['PY_' + n])
+
                 else:
                     done[n] = item = ""
+
                 if found:
                     after = value[m.end():]
                     value = value[:m.start()] + item + after
                     if "$" in after:
                         notdone[name] = value
                     else:
-                        try: value = int(value)
+                        try:
+                            value = int(value)
                         except ValueError:
                             done[name] = value.strip()
                         else:
                             done[name] = value
-                        del notdone[name]
+                        variables.remove(name)
+
+                        if name.startswith('PY_') \
+                        and name[3:] in renamed_variables:
+
+                            name = name[3:]
+                            if name not in done:
+                                done[name] = value
+
+
             else:
-                # bogus variable reference; just drop it since we can't deal
-                del notdone[name]
+                # bogus variable reference (e.g. "prefix=$/opt/python");
+                # just drop it since we can't deal
+                done[name] = value
+                variables.remove(name)
+
     # strip spurious spaces
     for k, v in done.items():
         if isinstance(v, str):
Index: b/Makefile.pre.in
===================================================================
--- a/Makefile.pre.in
+++ b/Makefile.pre.in
@@ -68,12 +68,18 @@ MAKESETUP=      $(srcdir)/Modules/makese
 # Compiler options
 OPT=		@OPT@
 BASECFLAGS=	@BASECFLAGS@
-CFLAGS=		$(BASECFLAGS) @CFLAGS@ $(OPT) $(EXTRA_CFLAGS)
+CONFIGURE_CFLAGS=	@CFLAGS@
+CONFIGURE_CPPFLAGS=	@CPPFLAGS@
+CONFIGURE_LDFLAGS=	@LDFLAGS@
+# Avoid assigning CFLAGS, LDFLAGS, etc. so users can use them on the
+# command line to append to these values without stomping the pre-set
+# values.
+PY_CFLAGS=	$(BASECFLAGS) $(OPT) $(CONFIGURE_CFLAGS) $(CFLAGS) $(EXTRA_CFLAGS)
 # Both CPPFLAGS and LDFLAGS need to contain the shell's value for setup.py to
 # be able to build extension modules using the directories specified in the
 # environment variables
-CPPFLAGS=	-I. -IInclude -I$(srcdir)/Include @CPPFLAGS@
-LDFLAGS=	@LDFLAGS@
+PY_CPPFLAGS=	-I. -IInclude -I$(srcdir)/Include $(CONFIGURE_CPPFLAGS) $(CPPFLAGS)
+PY_LDFLAGS=	$(CONFIGURE_LDFLAGS) $(LDFLAGS)
 LDLAST=		@LDLAST@
 SGI_ABI=	@SGI_ABI@
 CCSHARED=	@CCSHARED@
@@ -82,7 +88,7 @@ ARFLAGS=	@ARFLAGS@
 # Extra C flags added for building the interpreter object files.
 CFLAGSFORSHARED=@CFLAGSFORSHARED@
 # C flags used for building the interpreter object files
-PY_CFLAGS=	$(CFLAGS) $(CPPFLAGS) $(CFLAGSFORSHARED) -DPy_BUILD_CORE
+PY_CORE_CFLAGS=	$(PY_CFLAGS) $(PY_CPPFLAGS) $(CFLAGSFORSHARED) -DPy_BUILD_CORE
 
 
 # Machine-dependent subdirectories
@@ -437,7 +443,7 @@ coverage:
 
 # Build the interpreter
 $(BUILDPYTHON):	Modules/python.o $(LIBRARY) $(LDLIBRARY)
-		$(LINKCC) $(LDFLAGS) $(LINKFORSHARED) -o $@ \
+		$(LINKCC) $(PY_LDFLAGS) $(LINKFORSHARED) -o $@ \
 			Modules/python.o \
 			$(BLDLIBRARY) $(LIBS) $(MODLIBS) $(SYSLIBS) $(LDLAST)
 
@@ -469,7 +475,7 @@ sharedmods: $(BUILDPYTHON) pybuilddir.tx
 	    *\ -s*|s*) quiet="-q";; \
 	    *) quiet="";; \
 	esac; \
-	$(RUNSHARED) CC='$(CC)' LDSHARED='$(BLDSHARED)' OPT='$(OPT)' \
+	$(RUNSHARED) CC='$(CC)' LDSHARED='$(BLDSHARED)' LDFLAGS='$(PY_LDFLAGS)' OPT='$(OPT)' \
 		_TCLTK_INCLUDES='$(TCLTK_INCLUDES)' _TCLTK_LIBS='$(TCLTK_LIBS)' \
 		$(PYTHON_FOR_BUILD) $(srcdir)/setup.py $$quiet build
 
@@ -487,18 +493,18 @@ $(LIBRARY): $(LIBRARY_OBJS)
 
 libpython$(VERSION).so: $(LIBRARY_OBJS)
 	if test $(INSTSONAME) != $(LDLIBRARY); then \
-		$(BLDSHARED) -Wl,-h$(INSTSONAME) -o $(INSTSONAME) $(LIBRARY_OBJS) $(MODLIBS) $(SHLIBS) $(LIBC) $(LIBM) $(LDLAST); \
+		$(BLDSHARED) $(PY_LDFLAGS) -Wl,-h$(INSTSONAME) -o $(INSTSONAME) $(LIBRARY_OBJS) $(MODLIBS) $(SHLIBS) $(LIBC) $(LIBM) $(LDLAST); \
 		$(LN) -f $(INSTSONAME) $@; \
 	else \
-		$(BLDSHARED) -o $@ $(LIBRARY_OBJS) $(MODLIBS) $(SHLIBS) $(LIBC) $(LIBM) $(LDLAST); \
+		$(BLDSHARED) $(PY_LDFLAGS) -o $@ $(LIBRARY_OBJS) $(MODLIBS) $(SHLIBS) $(LIBC) $(LIBM) $(LDLAST); \
 	fi
 
 libpython$(VERSION).dylib: $(LIBRARY_OBJS)
-	 $(CC) -dynamiclib -Wl,-single_module $(LDFLAGS) -undefined dynamic_lookup -Wl,-install_name,$(prefix)/lib/libpython$(VERSION).dylib -Wl,-compatibility_version,$(VERSION) -Wl,-current_version,$(VERSION) -o $@ $(LIBRARY_OBJS) $(SHLIBS) $(LIBC) $(LIBM) $(LDLAST); \
+	 $(CC) -dynamiclib -Wl,-single_module $(PY_LDFLAGS) -undefined dynamic_lookup -Wl,-install_name,$(prefix)/lib/libpython$(VERSION).dylib -Wl,-compatibility_version,$(VERSION) -Wl,-current_version,$(VERSION) -o $@ $(LIBRARY_OBJS) $(SHLIBS) $(LIBC) $(LIBM) $(LDLAST); \
 
 
 libpython$(VERSION).sl: $(LIBRARY_OBJS)
-	$(LDSHARED) -o $@ $(LIBRARY_OBJS) $(MODLIBS) $(SHLIBS) $(LIBC) $(LIBM) $(LDLAST)
+	$(LDSHARED) $(PY_LDFLAGS) -o $@ $(LIBRARY_OBJS) $(MODLIBS) $(SHLIBS) $(LIBC) $(LIBM) $(LDLAST)
 
 # Copy up the gdb python hooks into a position where they can be automatically
 # loaded by gdb during Lib/test/test_gdb.py
@@ -537,7 +543,7 @@ $(PYTHONFRAMEWORKDIR)/Versions/$(VERSION
 # for a shared core library; otherwise, this rule is a noop.
 $(DLLLIBRARY) libpython$(VERSION).dll.a: $(LIBRARY_OBJS)
 	if test -n "$(DLLLIBRARY)"; then \
-		$(LDSHARED) -Wl,--out-implib=$@ -o $(DLLLIBRARY) $^ \
+		$(LDSHARED) $(PY_LDFLAGS) -Wl,--out-implib=$@ -o $(DLLLIBRARY) $^ \
 			$(LIBS) $(MODLIBS) $(SYSLIBS) $(LDLAST); \
 	else true; \
 	fi
@@ -581,7 +587,7 @@ Modules/getbuildinfo.o: $(PARSER_OBJS) \
 		$(SIGNAL_OBJS) \
 		$(MODOBJS) \
 		$(srcdir)/Modules/getbuildinfo.c
-	$(CC) -c $(PY_CFLAGS) \
+	$(CC) -c $(PY_CORE_CFLAGS) \
 	      -DSVNVERSION="\"`LC_ALL=C $(SVNVERSION)`\"" \
 	      -DHGVERSION="\"`LC_ALL=C $(HGVERSION)`\"" \
 	      -DHGTAG="\"`LC_ALL=C $(HGTAG)`\"" \
@@ -589,7 +595,7 @@ Modules/getbuildinfo.o: $(PARSER_OBJS) \
 	      -o $@ $(srcdir)/Modules/getbuildinfo.c
 
 Modules/getpath.o: $(srcdir)/Modules/getpath.c Makefile
-	$(CC) -c $(PY_CFLAGS) -DPYTHONPATH='"$(PYTHONPATH)"' \
+	$(CC) -c $(PY_CORE_CFLAGS) -DPYTHONPATH='"$(PYTHONPATH)"' \
 		-DPREFIX='"$(prefix)"' \
 		-DEXEC_PREFIX='"$(exec_prefix)"' \
 		-DVERSION='"$(VERSION)"' \
@@ -597,7 +603,7 @@ Modules/getpath.o: $(srcdir)/Modules/get
 		-o $@ $(srcdir)/Modules/getpath.c
 
 Modules/python.o: $(srcdir)/Modules/python.c
-	$(MAINCC) -c $(PY_CFLAGS) -o $@ $(srcdir)/Modules/python.c
+	$(MAINCC) -c $(PY_CORE_CFLAGS) -o $@ $(srcdir)/Modules/python.c
 
 Modules/posixmodule.o: $(srcdir)/Modules/posixmodule.c $(srcdir)/Modules/posixmodule.h
 
@@ -614,7 +620,7 @@ $(GRAMMAR_C): $(GRAMMAR_H) $(GRAMMAR_INP
 		touch $(GRAMMAR_C)
 
 $(PGEN):	$(PGENOBJS)
-		$(CC) $(OPT) $(LDFLAGS) $(PGENOBJS) $(LIBS) -o $(PGEN)
+		$(CC) $(OPT) $(PY_LDFLAGS) $(PGENOBJS) $(LIBS) -o $(PGEN)
 
 Parser/grammar.o:	$(srcdir)/Parser/grammar.c \
 				$(srcdir)/Include/token.h \
@@ -636,10 +642,10 @@ $(AST_C): $(AST_ASDL) $(ASDLGEN_FILES)
 Python/compile.o Python/symtable.o Python/ast.o: $(GRAMMAR_H) $(AST_H)
 
 Python/getplatform.o: $(srcdir)/Python/getplatform.c
-		$(CC) -c $(PY_CFLAGS) -DPLATFORM='"$(MACHDEP)"' -o $@ $(srcdir)/Python/getplatform.c
+		$(CC) -c $(PY_CORE_CFLAGS) -DPLATFORM='"$(MACHDEP)"' -o $@ $(srcdir)/Python/getplatform.c
 
 Python/importdl.o: $(srcdir)/Python/importdl.c
-		$(CC) -c $(PY_CFLAGS) -I$(DLINCLDIR) -o $@ $(srcdir)/Python/importdl.c
+		$(CC) -c $(PY_CORE_CFLAGS) -I$(DLINCLDIR) -o $@ $(srcdir)/Python/importdl.c
 
 Objects/unicodectype.o:	$(srcdir)/Objects/unicodectype.c \
 				$(srcdir)/Objects/unicodetype_db.h
@@ -1244,7 +1250,7 @@ config.status:	$(srcdir)/configure
 
 # Some make's put the object file in the current directory
 .c.o:
-	$(CC) -c $(PY_CFLAGS) -o $@ $<
+	$(CC) -c $(PY_CORE_CFLAGS) -o $@ $<
 
 # Run reindent on the library
 reindent:
Index: b/Modules/makesetup
===================================================================
--- a/Modules/makesetup
+++ b/Modules/makesetup
@@ -219,7 +219,7 @@ sed -e 's/[ 	]*#.*//' -e '/^[ 	]*$/d' |
 			case $doconfig in
 			no)	cc="$cc \$(CCSHARED) \$(CFLAGS) \$(CPPFLAGS)";;
 			*)
-				cc="$cc \$(PY_CFLAGS)";;
+				cc="$cc \$(PY_CORE_CFLAGS)";;
 			esac
 			rule="$obj: $src; $cc $cpps -c $src -o $obj"
 			echo "$rule" >>$rulesf
Index: b/configure.ac
===================================================================
--- a/configure.ac
+++ b/configure.ac
@@ -610,14 +610,13 @@ if test "$MACHDEP" = "irix6" && test "$C
     fi
 fi
 
-# If the user set CFLAGS, use this instead of the automatically
-# determined setting
-preset_cflags="$CFLAGS"
-AC_PROG_CC
-if test ! -z "$preset_cflags"
-then
-	CFLAGS=$preset_cflags
+# Don't let AC_PROG_CC set the default CFLAGS. It normally sets -g -O2
+# when the compiler supports them, but we don't always want -O2, and
+# we set -g later.
+if test -z "$CFLAGS"; then
+        CFLAGS=
 fi
+AC_PROG_CC
 
 AC_SUBST(CXX)
 AC_SUBST(MAINCC)
Index: b/Lib/distutils/sysconfig.py
===================================================================
--- a/Lib/distutils/sysconfig.py
+++ b/Lib/distutils/sysconfig.py
@@ -320,11 +320,19 @@ def parse_makefile(fn, g=None):
                     done[n] = v
 
     # do variable interpolation here
-    while notdone:
-        for name in notdone.keys():
+    variables = list(notdone.keys())
+
+    # Variables with a 'PY_' prefix in the makefile. These need to
+    # be made available without that prefix through sysconfig.
+    # Special care is needed to ensure that variable expansion works, even
+    # if the expansion uses the name without a prefix.
+    renamed_variables = ('CFLAGS', 'LDFLAGS', 'CPPFLAGS')
+
+    while len(variables) > 0:
+        for name in tuple(variables):
             value = notdone[name]
             m = _findvar1_rx.search(value) or _findvar2_rx.search(value)
-            if m:
+            if m is not None:
                 n = m.group(1)
                 found = True
                 if n in done:
@@ -335,25 +343,47 @@ def parse_makefile(fn, g=None):
                 elif n in os.environ:
                     # do it like make: fall back to environment
                     item = os.environ[n]
+
+                elif n in renamed_variables:
+                    if name.startswith('PY_') and name[3:] in renamed_variables:
+                        item = ""
+
+                    elif 'PY_' + n in notdone:
+                        found = False
+
+                    else:
+                        item = str(done['PY_' + n])
+
                 else:
                     done[n] = item = ""
+
                 if found:
                     after = value[m.end():]
                     value = value[:m.start()] + item + after
                     if "$" in after:
                         notdone[name] = value
                     else:
-                        try: value = int(value)
+                        try:
+                            value = int(value)
                         except ValueError:
                             done[name] = value.strip()
                         else:
                             done[name] = value
-                        del notdone[name]
-            else:
-                # bogus variable reference; just drop it since we can't deal
-                del notdone[name]
+                        variables.remove(name)
+
+                        if name.startswith('PY_') \
+                        and name[3:] in renamed_variables:
 
-    fp.close()
+                            name = name[3:]
+                            if name not in done:
+                                done[name] = value
+
+
+            else:
+                # bogus variable reference (e.g. "prefix=$/opt/python");
+                # just drop it since we can't deal
+                done[name] = value
+                variables.remove(name)
 
     # strip spurious spaces
     for k, v in done.items():