Add define to use customize vulkan header.

Bug: skia:
Change-Id: Ia87c81a54603a02b2f8f51a735bf173a49afe6c7
Reviewed-on: https://skia-review.googlesource.com/81121
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
3 files changed