Use clang on mac if XCode >= 4.5

tools/gyp/find_mac_gcc_version.py

Index: tools/gyp/find_mac_gcc_version.py
diff --git a/tools/gyp/find_mac_gcc_version.py b/tools/gyp/find_mac_gcc_version.py
index 0af84120b6b22e9d1fa09b094252090c345124b9..1f136ddce8eb62dcb13c192309c4a94f7c4958a0 100755
--- a/tools/gyp/find_mac_gcc_version.py
+++ b/tools/gyp/find_mac_gcc_version.py
@@ -21,10 +21,13 @@ def main():
     major = int(matches[0][0])
     minor = int(matches[0][1])
 
-    if major >= 4:
-      return 'com.apple.compilers.llvmgcc42'
-    elif major == 3 and minor >= 1:
+    if major == 3 and minor >= 1:
       return '4.2'
+    elif major == 4 and minor < 5:
+      return 'com.apple.compilers.llvmgcc42'
+    elif major == 4 and minor >= 5:
+      # XCode seems to select the specific clang version automatically
+      return 'com.apple.compilers.llvm.clang.1_0'
     else:
       raise Exception('Unknown XCode Version "%s"' % version_match)
   else: