Bazel sets the environment variable TEST_WARNINGS_OUTPUT_FILE
https://bazel.build/reference/test-encyclopedia#initial-conditions
If no tests are linked and the new flag --gtest_fail_if_no_test_linked
is not true (which is the current default), we can still warn the user
as this may be a programming error without failing the test (which would
break existing users).
PiperOrigin-RevId: 731402363
Change-Id: Ia481689efd4bd18889feaaa38bc56049a3f651cd