replace platform conditions with os_posix and os_bsd where applicable

ppapi/ppapi_internal.gyp

Index: ppapi/ppapi_internal.gyp
diff --git a/ppapi/ppapi_internal.gyp b/ppapi/ppapi_internal.gyp
index 3ee98fc8b214e47bb801bddd3d267de89629431f..977c7eecc1e479ed34f4071ac48acd57c7b20ba0 100644
--- a/ppapi/ppapi_internal.gyp
+++ b/ppapi/ppapi_internal.gyp
@@ -13,7 +13,7 @@
       # 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,