[build]: Replace fatal errors with conditional warnings for Clipboard Image Support

[evertonse]

Fixes #4459

Conditional compilation warnings instead of warnings to inform developers about the necessary dependencies when enabling clipboard image support (e.g. SUPPORT_MODULE_RTEXTURES, specific image formats , etc ...).

This allows for more flexible configuration while still alerting users, although subtely.

NOTE: 6.10.7 C standard says that any unrecognized #pragma should be ignored, so it should be no problem is case of less common C compilers.

[raysan5]

@evertonse Merging this review but maybe it will be redesigned, I usually try to avoid/minimize #pragma errors/warnings in raylib... but I need to think about it...

[evertonse]

@evertonse Merging this review but maybe it will be redesigned, I usually try to avoid/minimize #pragma errors/warnings in raylib... but I need to think about it...

That's completely fine.

A better solution might be to pull all the dependencies inside rcore.c itsself, as I suggested here, because it seems that building with cmake -DCUSTOMIZE_BUILD it doesn't pull config.h, I might be wrong but it seems that way.

[raysan5]

@evertonse config.h didn't force any flags, just define the user desired ones (but lately some conditionals were added).

The approach usually used on raylib was just checking required flag availability at a function level and fail gracefully with a TraceLog(LOG_WARNING, ...) message. It's up to the user to enable required/desired flags.