add a check and only set up and build compiler-rt builtins if they have
not been disabled
Index: llvm-toolchain-snapshot_21~++20250630094904+57f7e14b5779/llvm/runtimes/CMakeLists.txt
===================================================================
--- llvm-toolchain-snapshot_21~++20250630094904+57f7e14b5779.orig/llvm/runtimes/CMakeLists.txt
+++ llvm-toolchain-snapshot_21~++20250630094904+57f7e14b5779/llvm/runtimes/CMakeLists.txt
@@ -144,10 +144,15 @@ endfunction()
 # is required because the other runtimes need the builtin libraries present
 # before the just-built compiler can pass the configuration tests.
 get_compiler_rt_path(compiler_rt_path)
-if(compiler_rt_path)
+# check if builtins have been disabled
+set(RUNTIMES_BUILD_BUILTINS ON)
+if(DEFINED COMPILER_RT_BUILD_BUILTINS)
+  set(RUNTIMES_BUILD_BUILTINS ${COMPILER_RT_BUILD_BUILTINS})
+endif()
+if(compiler_rt_path AND RUNTIMES_BUILD_BUILTINS)
   # If the user did not specify the targets infer them from the runtimes.
   set(builtin_targets ${LLVM_BUILTIN_TARGETS})
-  if(NOT builtin_targets)
+  if(NOT LLVM_BUILTIN_TARGETS)
     if("compiler-rt" IN_LIST LLVM_ENABLE_RUNTIMES)
       list(APPEND builtin_targets "default")
     endif()