contrib: Skip libstdc++ files in check_GNU_style.py

The libstdc++ style is different from the rest of GCC, so do not apply
the checks to libstdc++ files in a patch.

contrib/ChangeLog:

	* check_GNU_style_lib.py (check_GNU_style_file): Do not check
	libstdc++ files.

Reviewed-by: Christophe Lyon <christophe.lyon@linaro.org>

contrib/check_GNU_style_lib.py

@@ -285,6 +285,9 @@ def check_GNU_style_file(file, format):
         # Skip testsuite files
         if 'testsuite' in t or t.endswith('.py'):
             continue
+        # Libstdc++ does not use GNU style
+        if t.startswith('libstdc++-v3/'):
+            continue
 
         for hunk in pfile:
             delta = 0