Import GoogleTest 1.14.0

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