android: util: add log.c to Makefile.sources
Fixes the following building errors:
external/mesa/src/intel/vulkan/anv_android.c:627: error: undefined reference to 'mesa_log' ... external/mesa/src/intel/vulkan/anv_device.c:164: error: undefined reference to 'mesa_log'
Fixes: 13ea7db7 ("mesa: Promote Intel's simple logging façade for Android to util/") Signed-off-by: Mauro Rossi issor.oruam@gmail.com