[cfe-commits] Add gTest unittests to clang, and write the first one. (issue4063046)

[jyasskin at gmail.com]

Reviewers: daniel_zuster.org,

Message:
Please take a look.

Description:
This doesn't include the cmake build steps, but it should let us start
writing library-based tests with the plain makefiles.

Please review this at http://codereview.appspot.com/4063046/

Affected files:
   M     Makefile
   M     test/Makefile
   A     test/Unit/lit.cfg
   A     test/Unit/lit.site.cfg.in
   A     unittests/Frontend/FrontendActionTest.cpp
   A     unittests/Frontend/Makefile
   A     unittests/Makefile