build-exe's -F to set compiler's -F cflag

[frarees]

Using zig build-exe -F <path> tells the linker to use -F <path>.

If you use custom framework locations (e.g. ./fwk/SDL2.framework), it would be useful to tell the compiler to -F <path> too, so that it can search for headers. Otherwise, you have to include them manually (e.g. -I./fwk/SDL2.framework/Headers).

Thoughts?