[gn] Move dsymutil from link command to a separate action

Change-Id: I18a3bd5e845305e3b2521d076fd641bd5175b618
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/234327
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Auto-Submit: Ben Wagner aka dogben <benjaminwagner@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
2 files changed