Disable building libobjc with clang as it's not yet supported.

Submitted by:	Dimitry Andric <dimitry at andric.com>

gnu/lib/libobjc/Makefile

@@ -13,6 +13,9 @@ SRCS=	archive.c class.c encoding.c gc.c hash.c init.c linking.m misc.c \
 	nil_method.c NXConstStr.m Object.m objects.c Protocol.m sarray.c \
 	selector.c sendmsg.c thr.c thr-objc.c exception.c
 
+# XXX: clang cannot compile libobjc yet
+CC:=${CC:C/^cc|^clang/gcc/}
+
 INCS=	encoding.h hash.h objc-api.h objc-decls.h objc-list.h objc.h runtime.h \
 	sarray.h thr.h typedstream.h NXConstStr.h Object.h Protocol.h
 INCSDIR=${INCLUDEDIR}/objc