[ios] Partially decouple iOS and macOS GN configuration.
Duplicates configs defined in //build/config/mac/BUILD.gn that
are shared with iOS to //build/config/ios/BUILD.gn. Remove all
conditions testing "is_mac" or "is_ios" (as they are now known
from the filename).
Change dependencies on previously shared targets to select the
correct target based on the "target_os".
BUG=635745
Review-Url: https://codereview.chromium.org/2843493002
Cr-Original-Commit-Position: refs/heads/master@{#467680}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 1982eef8e01ab5e8ce6aeba827faa54c8e88838a
6 files changed
