Ninja on mac and win should also read CFLAGS/CXXFLAGS.

test/cflags/gyptest-cflags.py

 #!/usr/bin/env python
 
 # Copyright (c) 2012 Google Inc. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """
 Verifies build of an executable with C++ define specified by a gyp define, and
 the use of the environment during regeneration when the gyp file changes.
 """
 
 import os
 import sys
 import TestGyp
 
 env_stack = []
 
 
 def PushEnv():
   env_copy = os.environ.copy()
   env_stack.append(env_copy)
 
 def PopEnv():
   os.environ.clear()
   os.environ.update(env_stack.pop())
 
-formats = ['make']
-if sys.platform.startswith('linux'):
-  # Only Linux ninja generator supports CFLAGS.
-  formats.append('ninja')
+formats = ['make', 'ninja']
 
 test = TestGyp.TestGyp(formats=formats)
 
 try:
   PushEnv()
   os.environ['CFLAGS'] = ''
   os.environ['GYP_CROSSCOMPILE'] = '1'
   test.run_gyp('cflags.gyp')
   test.build('cflags.gyp')
 finally:
@@ skipping 57 matching lines @@
   # We clear the environ after calling gyp.  When the auto-regeneration happens,
   # the same define should be reused anyway.  Reset to empty string first in
   # case the platform doesn't support unsetenv.
   PopEnv()
 
 
 expect = """FOO defined\n"""
 test.run_built_executable('cflags', stdout=expect)
 
 test.pass_test()