GN: match shell behavior for cc and cxx in is_clang.py

gn/is_clang.py

Index: gn/is_clang.py
diff --git a/gn/is_clang.py b/gn/is_clang.py
index 99173a004c521f8073f4c6faf2cb52e89120967f..a63111c7a97284fb9cefeea21fb768bee88037b6 100755
--- a/gn/is_clang.py
+++ b/gn/is_clang.py
@@ -9,8 +9,8 @@ import subprocess
 import sys
 cc,cxx = sys.argv[1:3]
 
-if ('clang' in subprocess.check_output([cc,  '--version']) and
-    'clang' in subprocess.check_output([cxx, '--version'])):
+if ('clang' in subprocess.check_output('%s --version' % cc, shell=True) and
+    'clang' in subprocess.check_output('%s --version' % cxx, shell=True)):
   print 'true'
 else:
   print 'false'