Add a `#warning` compile time proc that will be used for things that may or may not cause problems

[A-Boring-Square]

I need a way to warn users of my library when they enable a compile-time configuration flag that may not be supported on all systems.

I would like a compile-time procedure similar to #assert, but instead of stopping compilation, it would emit a warning or notification and allow compilation to continue.

This would be useful for APIs with optional behavior, such as OpenGL, where users can choose between core and compatibility profiles. Some features may not be available in one mode, but that should not prevent the application from compiling if the user intentionally chose that configuration.