* build: preserve timestamps when stripping files

Resolves an issue where the binaries in mksnapshot.zip were not getting stripped.

* Add missing comma

* Update script/strip-binaries.py

Co-Authored-By: Jeremy Apthorp <jeremya@chromium.org>

* Don't try to run strip on macOS

Co-authored-by: Jeremy Apthorp <nornagon@nornagon.net>