Update cxx_extractor to LLVM 12.0.3

Apply the following upstream patches:
https://github.com/kythe/kythe/pull/4743/commits/57bceba9848f911d6e2c7db57a2f203c07c01bf4
https://github.com/kythe/kythe/pull/4723/commit/4ab0b101b19ca582903b596c5562ed7ce6fc95ca.patch
(only the C++ files have been patched)

Bug: 180760045
Test: build, the use to build kzips
Change-Id: Iea3ad15cd1e30c824f280f2c2bb085bf875869b3
4 files changed