Older branches of Android don't support std::unordered_map.

Bug 28006371

Change-Id: I162249db3b7ee9537c7143768c6c1ec216392cba
Reviewed-on: https://swiftshader-review.googlesource.com/5045Reviewed-by: Bo Hu <bohu@google.com>
Tested-by: Nicolas Capens <capn@google.com>
(cherry picked from commit db4fee2752c3b440933fd89078e35b3781c211ce)
Reviewed-on: https://swiftshader-review.googlesource.com/5047Reviewed-by: Nicolas Capens <capn@google.com>