This is needed for building on MinGW.

Bug: angleproject:3330
Change-Id: I4a7e7d6f6e14be7e1ba67d3ceb45b11d00585119
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1544749Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>