Popped up when testing with the new compiler.

Bug: angleproject:3986
Change-Id: I2c0f838941b133e0d7785f1ba62b5e7d02d89bd4
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1849986Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>