Use C++17 attributes instead of custom macros Bug: angleproject:6747 Change-Id: Iad6c7cd8a18d028e01da49b647c5d01af11e0522 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3718999 Reviewed-by: Cody Northrop <cnorthrop@google.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>