Suppress preprocessor warnings

[copyrat90]

When you use #pragma once for your header file, and include that header as TEXTS := in your Makefile,
butano_fonts_tool.py will spit this warning:

include/texts.h:5:9: warning: '#pragma once' in main file [-Wpragma-once-outside-header]
    5 | #pragma once
      |         ^~~~

This is obviously a false positive.

And in my opinion, all warnings should be disabled for this text pre-processing phase, because you would get warnings on project build time anyways.

So, this commit silences all the warnings when process_texts_files() executes C preprocessor.

[Copilot]

Pull Request Overview

This PR suppresses preprocessor warnings when processing text files that contain C/C++ headers by adding the -w flag to C preprocessor calls. The change addresses false positive warnings like #pragma once in main file warnings that occur during text preprocessing, since actual project warnings will be caught during the normal build process.

• Added -w flag to suppress all warnings during C preprocessor execution
• Applied the change to both DEVKITARM and WONDERFUL_TOOLCHAIN code paths

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