In an Apple-style build, compile with llvm-gcc/llvm-g++ if available.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@76080 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/buildit/build_llvm b/utils/buildit/build_llvm
index eac68b4..e574ff7 100755
--- a/utils/buildit/build_llvm
+++ b/utils/buildit/build_llvm
@@ -56,8 +56,11 @@
 DARWIN_VERS=`uname -r | sed 's/\..*//'`
 echo DARWIN_VERS = $DARWIN_VERS
 
-# If the user has CC set in their environment unset it now
-unset CC
+# If we can find an LLVM-GCC, prefer it.
+export CC=/Developer/usr/bin/llvm-gcc
+if [ ! -x $CC ] ; then unset CC ; fi
+export CXX=/Developer/usr/bin/llvm-g++
+if [ ! -x $CXX ] ; then unset CXX ; fi
 
 DT_HOME=$DEST_DIR/Developer/usr
 DEST_ROOT="/Developer$DEST_ROOT"