Add special case for mac clang version number

tool

@@ -125,7 +125,10 @@ cc_vers=
 lld_detected=0
 if cc_vers=$(echo -e '#ifndef __clang__\n#error Not found\n#endif\n__clang_major__.__clang_minor__.__clang_patchlevel__' | "$cc_exe" -E -xc - 2>/dev/null | tail -n 1 | tr -d '\040'); then
   cc_id=clang
-  if [[ $os != mac ]]; then
+  # Mac clang/llvm doesn't say the real version of clang. Just assume it's 3.9.0
+  if [[ $os == mac ]]; then
+    cc_vers=4.2.1
+  else
     if command -v "lld" >/dev/null 2>&1; then
       lld_detected=1
     fi