Fix gyptest-xcode-gcc.py when using Xcode 5.0.2

test/mac/gyptest-xcode-gcc.py

Index: test/mac/gyptest-xcode-gcc.py
diff --git a/test/mac/gyptest-xcode-gcc.py b/test/mac/gyptest-xcode-gcc.py
index abd884897d527c668d0165bd1690df7ab78408f2..e45d0b5e8bc0c57c06e80966d209d5bab94139e5 100644
--- a/test/mac/gyptest-xcode-gcc.py
+++ b/test/mac/gyptest-xcode-gcc.py
@@ -11,11 +11,23 @@ Verifies that xcode-style GCC_... settings are handled properly.
 import TestGyp
 
 import os
+import subprocess
 import sys
 
 def IgnoreOutput(string, expected_string):
   return True
 
+def CompilerVersion(compiler):
+  stdout = subprocess.check_output([compiler, '-v'], stderr=subprocess.STDOUT)
+  return stdout.rstrip('\n')
+
+def CompilerSupportsWarnAboutInvalidOffsetOfMacro(test):
+  # "clang" does not support the "-Winvalid-offsetof" flag, and silently
+  # ignore it. Starting with Xcode 5.0.0, "gcc" is just a "clang" binary with
+  # some hard-coded include path hack, so use the output of "-v" to detect if
+  # the compiler supports the flag or not.
+  return 'clang' not in CompilerVersion('/usr/bin/cc')
+
 if sys.platform == 'darwin':
   test = TestGyp.TestGyp(formats=['ninja', 'make', 'xcode'])
 
@@ -30,11 +42,7 @@ if sys.platform == 'darwin':
 
   # clang doesn't warn on invalid offsetofs, it silently ignores
   # -Wno-invalid-offsetof.
-  # TODO(thakis): This isn't really the right way to detect the compiler,
-  # Xcode has some embedded compiler, but it's a reliable proxy at least on
-  # the bots. The compiler is forced to gcc/g++ in the gyp file in a
-  # make_global_settings section for ninja and make.
-  if test.format != 'xcode' or os.readlink('/usr/bin/cc') != 'clang':
+  if CompilerSupportsWarnAboutInvalidOffsetOfMacro(test):
     targets.append('warn_about_invalid_offsetof_macro')
 
   for target in targets: