This results in calls like this added to Setup*:

    const GLenum glDrawBuffers_bufs_38[] =
        { 36064, 36065, 36066, 36067, 0, 0, 0, 0 };
    ...
    glDrawBuffers(8, glDrawBuffers_bufs_38);

Test: Aztec Ruins MEC
Bug: b/160808198
Bug: angleproject:3662
Bug: angleproject:5541
Change-Id: I1c6282e292f225684c99b5de65daf8ad15b0db56
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2627907Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Cody Northrop <cnorthrop@google.com>