Build protobuf for PNacl.

This adds protobuf_lite_nacl that compiles protobuf_lite for PNaCl.

BUG=276739

Review URL: https://codereview.chromium.org/137533018

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247172 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247172