Fix GoogleTest 1.14.0 import

- Prune headers and tests no longer installed after the upgrade.
- Remove GoogleTest-related files when MK_GOOGLETEST == no.
- Disable `-Werror` with gcc to unbreak the gcc12 CI run with
  `lib/googletest`. Any issues found by g++ will be filed
  upstream and hopefully resolved in a future version.
- Remove clang -Werror issues which are resolved in version 1.14.0 to
  avoid masking valid issues.

MFC after:	1 week
MFC with:	28f6c2f292

share/mk/googletest.test.inc.mk

@@ -1,4 +1,3 @@
-
 GTESTS_CXXFLAGS+= -DGTEST_HAS_POSIX_RE=1
 GTESTS_CXXFLAGS+= -DGTEST_HAS_PTHREAD=1
 GTESTS_CXXFLAGS+= -DGTEST_HAS_STREAM_REDIRECTION=1
@@ -6,16 +5,6 @@ GTESTS_CXXFLAGS+= -frtti
 
 .include <bsd.compiler.mk>
 
-.if ${COMPILER_TYPE} == "clang" && ${COMPILER_VERSION} >= 100000
-# Required until googletest is upgraded to a more recent version (after
-# upstream commit efecb0bfa687cf87836494f5d62868485c00fb66).
-GTESTS_CXXFLAGS+= -Wno-deprecated-copy
-
-# Required until googletest is upgraded to a more recent version (after
-# upstream commit d44b137fd104dfffdcdea103f7de11b9eccc45c2).
-GTESTS_CXXFLAGS+= -Wno-signed-unsigned-wchar
-.endif
-
 # XXX: src.libnames.mk should handle adding this directory for libgtest's,
 # libgmock's, etc, headers.
 CXXFLAGS+=	-I${DESTDIR}${INCLUDEDIR}/private