Use Xcode relative compilers when possible

llvm-svn: 151108
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: d9d5b4492b93ff0d79b37fe82d47e7df5daaa4bc
diff --git a/test/testit b/test/testit
index d30e78c..774f96f 100755
--- a/test/testit
+++ b/test/testit
@@ -10,7 +10,12 @@
 
 if [ -z $CC ]
 then
-	CC=clang++
+	if which xcrun >/dev/null
+	then
+		CC="xcrun clang++"
+	else
+		CC=clang++
+	fi
 fi
 
 if [ -z "$OPTIONS" ]