Support .cxx as valid file name extension for source code.
Support .cxx as valid file name extension for source code.

This enables the tiff library build

BUG= http://code.google.com/p/naclports/issues/detail?id=27
Review URL: http://codereview.chromium.org/9147046

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@7551 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

sbc100/native_client,nacl-webkit/native_client,sbc100/native_client,nacl-webkit/native_client,nacl-webkit/native_client,nacl-webkit/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client