generate_android_bp.py: Don't include buildtools/third_party/libc++/ The buildtools/ directory is not included in the AOSP version of ANGLE and is unnecessary, so update generate_android_bp.py to filter out that include directory. Bug: b/187342779 Change-Id: I3a2d0506ac53f7d369597c797fffb211ffde41f1 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2995382 Reviewed-by: Tim Van Patten <timvp@google.com> Commit-Queue: Tim Van Patten <timvp@google.com>