[LTC] Fix a few build issues in my environment (#67034)
- clang 11 doesn't support `-Wno-error=maybe-uninitialized`. Just
replace it with `-Wno-error` (I don't think we care that much about
googletest's warnings -- we could silence all warnings with `-w`
potentially as well).
- Use `cmake --build` instead of hardcoding `make` in `run_tests.sh`.
This makes it more portable across cmake generators (I have been using
ninja)
- Add a separate `cmake --build` invocation for `googletest` to appease
the CMake Ninja generator. I'm not sure why it requires this.
