-Wsuggest-destructor-override and -Wsuggest-override.

Bug: skia:7647
Change-Id: Iaac1baa8f34fdf210baf2fdbe811a582b3ac2d14
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2376717Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>