[CMake] Where do add_dependencies() that are not defines go?

[Luke Dalessandro]

We sometimes use add_dependencies to add compile flags that aren't
defines, e.g., -m64. I am trying to build an add_custom_command that
needs access to these flags, but I can't seem to find them anywhere (I
can get the dependencies from the directory properties).

Does anyone know where these other flag types are stored?

Thanks,
Luke