[build][Zig] Fix raygui inclusion in windows cross compilation

[kimierik]

Problem:

Cross compiling to windows when adding Raygui would error due to how zig handles the C #include macro.

Solution:

Added explicit include path for raylib.h for the raylib dependency when adding raygui.

Extra Info:

• Build and executable tested only on my local machine.
• Only tested with argument -Dtarget=x86_64-windows

[deathbeam]

wouldnt it be better to just get rid of addRaygui and provide the raygui dependency reference as parameter in options (e.g the approach i started, but this part wasnt finished)? That should be possible I think. Instead of trying to make addRaygui work.

EDIT:

Looks like passing the dependency via options is indeed not possible. Maybe just adding the raygui dependency to build.zig.zon and simply making it lazy and optional makes most sense?

EDIT2:

Benefit of having the raygui dep in build.zig.zon directly is also that user will always have actual functional build instead of potentionally mismatched raylib and raygui versions

[kimierik]

Benefit of having the raygui dep in build.zig.zon directly is also that user will always have actual functional build instead of potentionally mismatched raylib and raygui versions

I dont think having raygui in the build.zig.zon is that good. The hash would have to be updated whenever raygui updates. And it could still lead to non functional builds if raylib updates and the raygui version has not.

I agree that addRaygui is not that good of a solution to the problem and a better alternative should be considered.

EDIT1:
If there is a way to get the pointer to the root build in the raylibs build.zig then it would be possible to use a boolean option to determine if raygui should be added. However AFAIK i dont think that is possible without giving it as a parameter of some sort, and then we would just have another fn that adds raygui.

In anycase this PR only fixes windows cross compile builds

[raysan5]

@kimierik thanks for the review!