[build] Suppress -Wunused-but-set-variable in mesa

This patch suppresses -Wunused-but-set-variable warning in
mesa third party code that does not comply with.

The code that causes the issues are as the following:
1)../../third_party/mesa/src/intel/compiler/brw_fs_cmod_propagation.cpp:226:8:
  error: variable 'ip' set but not used
2)../../third_party/mesa/src/intel/compiler/brw_schedule_instructions.cpp:1711:8:
  error: variable 'instructions_to_schedule' set but not used

Bug: 96410
Change-Id: I3e4b7af38e1ad5fb0ecad5e308ddb63d5818137e
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/mesa/+/663042
Reviewed-by: Petr Hosek <phosek@google.com>
1 file changed