Improve cross-compilation with zig builds

[deathbeam]

• Add xcode_frameworks when cross compiling for mac (ref: https://github.com/hexops/mach/blob/main/build.zig)
• Add emsdk when cross compiling for wasm (ref: https://github.com/floooh/sokol-zig/blob/master/build.zig)

[deathbeam]

For testing:

zig build -Doptimize=ReleaseFast -Dtarget=wasm32-emscripten
zig build -Doptimize=ReleaseFast -Dtarget=x86_64-macos

should just work ™️ with no external dependencies

[raysan5]

@deathbeam I don't like specially adding a separate .zig.zon file, more files usually mean more maintenance work and more breaking possibilities... but I'm merging it.

[deathbeam]

@deathbeam I don't like specially adding a separate .zig.zon file, more files usually mean more maintenance work and more breaking possibilities... but I'm merging it.

Yea if there was an option to put it to the build.zig i would do it but to use the zig dependency manager the zig.zon file is sadly necessary (at least afaik). but benefit is that when you use raylib as dependency in zig for other projects they will also get the 2 dependencies resolved at same time and cross-compilation should work for them out of the box as well (when set up properly).