Trying to fix gcc benchmark build: suppressing warning

23 jobs for multigrid-experiments in 136 minutes and 50 seconds (queued for 50 seconds)
Name Stage Failure
benchmark_gcc7 Test
CMakeFiles/Makefile2:13423: recipe for target 'apps/MultigridStudies/CMakeFiles/MultigridStudies.dir/all' failed
make[1]: *** [apps/MultigridStudies/CMakeFiles/MultigridStudies.dir/all] Error 2
Makefile:140: recipe for target 'all' failed
make: *** [all] Error 2

real 0m41.107s
user 5m30.194s
sys 0m35.099s
ERROR: Job failed: exit code 1