Trying to find a way to disable pragma warnings

[Jacob Brown]

I'm compile a project that uses -Wall, and it has a lot of warnings
from #pragmas caused by -Wunknown-pragmas.  So I've tried to disable
this by adding the pragama,
#pragma GCC diagnostic ignored "-Wunknown-pragmas"
This doesn't seem to work.  I've also tried adding -Wno-pragmas both
before and after -Wall on the command line CXX flags.

Anyone know what I'm doing wrong?

Thanks!