[CMake] Semi-related question

[Jonathan Hansen]

This more of a compiler question but I figured since people here are make
folks you might know and save me signing up for another list...

Is there a way in GCC to eliminate an include directory from warnings?

Example:

gcc -Wall -I/tmp/messycode foo.cpp foo.o

Where messycode will give a lot of known warnings I know about but do not
want to see, but I DO want to see -Wall etc for foo.cpp, I just do not want
to have to wade through messycode's warnings to see them.

And to make sure this is relevant here, and avoid inevitable next question,
does cmake have a tag or command for this in the include commands so it will
work on Xcode and Visual Studio as well?

Any help is appreciated.

Jonathan