Add migration code for no_exceptions configs.

The libc++ configs all enable exceptions to build. This change
adds code so that the build works with both the old and new configs.
Once http://crrev.com/c/773079 lands then we can go back and fix up
the code to use only the new 'compiler:no_exceptions' config.

Bug: 727437
Change-Id: If2fe0a74fb3fb27f65d4bd34cb5c1efa64d0e7ee
3 files changed