When linking against Mali 450 r6, errors like the following
can be seen:
../../../../lib/libpiglitutil_gl.so.0: undefined reference to `gbm_bo_unmap'
../../../../lib/libpiglitutil_gl.so.0: undefined reference to `gbm_bo_map'
collect2: error: ld returned 1 exit status
make[2]: *** [bin/point-sprite] Error 1
This is due to gbm_bo_map() and gbm_bo_unmap() being recently
added but not yet implemented by all graphics drivers.
Instead of relying on GBM's version, actually try to link
against those symbols.
