Build zig update replaced `defineCMacro()` with equivalent `root_module.addCMacro()`.

[pierrelgol]

This pr updates the build.zig files in the root directory and in the example directory. I don't think this needs to be merged right now, but, this is the change that I needed to do locally to get raylib to compile with the nightly release of the Zig compiler.

[HaxSam]

There is already a pr for that look https://github.com/raysan5/raylib/pull/4620/

[raysan5]

It seems this PR is a duplicate of referred one, closing this one.

[pierrelgol]

My bad I didn't even saw that someone already made a pr, sorry for disturbing.