mac and ios: Turn linker warnings into errors.

Bug: 747727
Change-Id: I33f44e3f4011873e193088796483ecdc48f7f05e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1720610
Reviewed-by: Mark Mentovai <mark@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Auto-Submit: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#681434}
1 file changed