Copy the D3D compiler dll in the GN build.

Change-Id: I773a411d07991d9ae160267eba8325c327146554
Reviewed-on: https://chromium-review.googlesource.com/229007
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: John Abd-El-Malek <jam@chromium.org>