require c++14 public headers

It occurred to me that we try to guarantee this but don't test it.
Luckily this public_headers_warnings_check target is a perfect spot.

Change-Id: Ie06732706ee80da798a9c3bda215d5a65f02b5bd
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/295856
Commit-Queue: Mike Klein <mtklein@google.com>
Commit-Queue: Derek Sollenberger <djsollen@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Auto-Submit: Mike Klein <mtklein@google.com>
1 file changed