GoogleTest 1.14.0 now requires C++14 to build. Change
`googletest.test.inc.mk` to reflect this requirement.
Adjust the build integration logic to handle the new version of
GoogleTest (add/remove headers/sources as needed).
Tighten down warnings via `CXXFLAGS.clang` instead of ignoring all
warnings. Some new warnings snuck in after I did my last round of fix
submissions upstream.
Also address some overlinking added in the previous version import by
removing superfluous libraries.
===============================
Expect WhenDynamicCastToTest.AmbiguousCast to fail
This change reapplies the expected failure from 1.10.0.
Ref: https://github.com/google/googletest/issues/2172
MFC after: 2 weeks
Reviewed by: asomers, emaste
Differential Revision: https://reviews.freebsd.org/D41399
Merge commit '8ef491440fcaec96f899d73e08873426c78583a4' into googletest-v1.14.0-import
