replace platform conditions with os_posix and os_bsd where applicable

ppapi/ppapi_internal.gyp

 # Copyright (c) 2010 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   'variables': {
     'chromium_code': 1,  # Use higher warning level.
   },
   'target_defaults': {
     'conditions': [
       # Linux shared libraries should always be built -fPIC.
       #
       # TODO(ajwong): For internal pepper plugins, which are statically linked
       # into chrome, do we want to build w/o -fPIC?  If so, how can we express
       # that in the build system?
-      ['OS=="linux" or OS=="openbsd" or OS=="freebsd" or OS=="solaris"', {
+      ['os_posix==1 and OS!="android" and OS!="mac"', {
         'cflags': ['-fPIC', '-fvisibility=hidden'],
 
         # This is needed to make the Linux shlib build happy. Without this,
         # -fvisibility=hidden gets stripped by the exclusion in common.gypi
         # that is triggered when a shared library build is specified.
         'cflags/': [['include', '^-fvisibility=hidden$']],
       }],
     ],
   },
   'includes': [
     '../native_client/build/untrusted.gypi',
     'ppapi_proxy.gypi',
     'ppapi_shared.gypi',
     'ppapi_tests.gypi',
   ],
 }