magma: fail when exporting semaphores to sync file descriptor

Until we support sync files, this patch allows ANGLE to avoid
external fences and make progress.

Bug:67565

Change-Id: I613537e4419ebbbdc8e21c80c1e7959d72564c1e
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/mesa/+/858799
Reviewed-by: John Bauman <jbauman@google.com>
2 files changed