GN: Fix one missing check for 'angle_has_build'. This was blocking using our GN files in Skia. Bug: angleproject:4046 Change-Id: I12887a53c5f92b0e00206f8d391a8d03433b5e6e Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1877475 Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>