Declaring it unconditionally seems to build fine on all other platforms.

Change-Id: I4c587d6ec47989f0d22588aca8883c4ef68f91c8
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1579917
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>