Add sh4 to the list of supported architectures.

--- a/configure.ac
+++ b/configure.ac
@@ -149,6 +149,7 @@
 	[tile*], [ARCHTYPE="tile"],
 	[hppa*], [ARCHTYPE="hppa"],
 	[m68k], [ARCHTYPE="m68k"],
+	[sh4], [ARCHTYPE="gcc"],
 	[ARCHTYPE="unknown"]
 )