As part of this update, GoogleTest is now using the Abseil flags
implementation, and the flags usage_test needs to be modified to pass.

If building with bazel and --define=absl=1 to force GoogleTest to use
Abseil, a WORKSPACE dependency on the abseil branch of the RE2 project
is now required.

PiperOrigin-RevId: 455512245
Change-Id: I2025df0c86006fac97a80713524c9d0aae8b358e