MAP_ANON has been deprecated in favor of MAP_ANONYMOUS, but Mac OS only
defines MAP_ANON.

Bug chromium:630728

Change-Id: I7345a5f9227acbc0caa29d8103855ab531f16499
Reviewed-on: https://swiftshader-review.googlesource.com/8531Reviewed-by: Alexis Hétu <sugoi@google.com>
Tested-by: Nicolas Capens <capn@google.com>