Make gyp.el conform to conventional library format

Makes it play better with Emacs ecosystem generally (e.g., builtin package.el support)

Change-Id: Ifb48baf85fcfdd71052e1a0098dc0b845417dc86
Reviewed-on: https://chromium-review.googlesource.com/c/external/gyp/+/5276479
Reviewed-by: Mark Mentovai <mark@chromium.org>