Fixes the following building errors:

In file included from external/mesa/src/gallium/drivers/freedreno/a3xx/fd3_query.c:27:
In file included from external/mesa/src/gallium/drivers/freedreno/freedreno_query_hw.h:33:
In file included from external/mesa/src/gallium/drivers/freedreno/freedreno_context.h:33:
external/mesa/src/util/libsync.h:48:10: fatal error: 'android/sync.h' file not found
         ^~~~~~~~~~~~~~~~
1 error generated.

In file included from external/mesa/src/mesa/drivers/dri/i965/brw_sync.c:41:
external/mesa/src/util/libsync.h:48:10: fatal error: 'android/sync.h' file not found
         ^~~~~~~~~~~~~~~~
1 error generated.

FAILED: out/target/product/x86_64/obj_x86/SHARED_LIBRARIES/i965_dri_intermediates/LINKED/i965_dri.so
...
external/mesa/src/mesa/drivers/dri/i965/brw_sync.c:223: error: undefined reference to 'sync_wait'
external/mesa/src/mesa/drivers/dri/i965/brw_sync.c:287: error: undefined reference to 'sync_wait'

FAILED: out/target/product/x86_64/obj_x86/SHARED_LIBRARIES/gallium_dri_intermediates/LINKED/gallium_dri.so
...
external/mesa/src/util/libsync.h:142: error: undefined reference to 'sync_merge'
external/mesa/src/util/libsync.h:142: error: undefined reference to 'sync_merge'
external/mesa/src/util/libsync.h:142: error: undefined reference to 'sync_merge'
external/mesa/src/util/libsync.h:142: error: undefined reference to 'sync_merge'
external/mesa/src/gallium/drivers/freedreno/freedreno_fence.c:94: error: undefined reference to 'sync_wait'
external/mesa/src/gallium/auxiliary/util/u_tests.c:575: error: undefined reference to 'sync_wait'
external/mesa/src/gallium/auxiliary/util/u_tests.c:578: error: undefined reference to 'sync_wait'
external/mesa/src/gallium/auxiliary/util/u_tests.c:579: error: undefined reference to 'sync_wait'

Fixes: 27b88879

 ("android: Add pre-4.7 Android kernel compatibility to our libsync header.")
Signed-off-by: Mauro Rossi <issor.oruam@gmail.com>