Ensure glxGetProcAddress is declared

Users on some systems reported that this was necessary.

Bug: skia:
Change-Id: I1e7f6c4859a34008c307256ab3d77265bdbe4f6b
Reviewed-on: https://skia-review.googlesource.com/55101
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
1 file changed