Also unify warning options across Clang and GCC and fix minor issues that was surfaced by this.
PiperOrigin-RevId: 508619655
Change-Id: I59b777bf2dfea4422485670e2427c7d3f5cf6405
Since upgrading to Clang 15, abseil fails to build, because of abseil/abseil-cpp#1201.
PiperOrigin-RevId: 486190797
Change-Id: Ibaa1c03b8d21ae4a83c3825c8d56363aa2f89505