Since !4125 (merged) CMake supports "fat" builds with different
sysroots. Those are passed to the compiler with the
Unfortunately this breaks the Compiler Cache (ccache) because it does not support those compiler flags: https://github.com/ccache/ccache/blob/v3.7.9/src/ccache.c#L2700-L2705
This change restores the caching ability for certain "fat" build
armv7) where the sysroot is the
same for all selected architectures and thus a plain
parameter could be used.