[tools] Add clean action to gm.py

Now you can also clean build directories: x64.optdebug.clean
Or clean and build: x64.release.clean.d8

No-Try: True
Change-Id: I3df59416d4ce7db5306c0b09c9ee8293c7a345f9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2964595


Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75176}