android: Add pre-4.7 Android kernel compatibility to our libsync header.

The downstream Android kernels had a different API than was merged
upstream, and libsync on Android abstracts over that for us.  Use their
sync_merge() and sync_wait(), at the cost of linking against libsync
(which Android.mk and meson both do).

Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6821>
1 file changed