This should fix the CFI build compatibility with class exports.

Bug: chromium:1030192
Bug: angleproject:3162
Change-Id: I228d6d387f8b29c0a500038de962f9f216454d7a
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1964933Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>