[rcore][android] Replace android_fopen() with linker --wrap=fopen

[ghera]

Context

This is a follow-up to #5589, which fixed LoadMusicStream failing on Android for OGG, WAV, and MP3 formats. That fix was accepted by @raysan5 as a temporary patch — adding a #define fopen android_fopen override directly inside raudio.c — with the hope of finding a cleaner solution.

As discussed in the comments of #5589, @maiconpintoabreu proposed this alternative approach: using the linker --wrap=fopen option to redirect all fopen calls at link time. This PR implements that approach.

What changed

• src/CMakeLists.txt: Added target_link_options(raylib INTERFACE -Wl,--wrap=fopen) for Android builds, so the linker redirects all fopen calls to __wrap_fopen transparently.
• src/Makefile: Added LDFLAGS += -Wl,--wrap=fopen.
• src/platforms/rcore_android.c: Renamed android_fopen → __wrap_fopen and added a __real_fopen declaration. Removed all #undef fopen inside the function body. Also fixes a missing fallback in write mode ('w'): the old code only tried internalDataPath/fileName; now falls back to the literal path if that fails, allowing absolute paths to work correctly.
• src/raudio.c: Removed the platform-specific #define fopen android_fopen block added in the previous patch.

Why this is better than the temporary patch

The macro approach only covered the source files that explicitly included the override. The linker --wrap=fopen covers all source files and third-party libraries simultaneously:

• LoadMusicStream() for OGG/WAV/MP3 — already fixed in via macro; now covered cleanly
• LoadOBJ() and LoadMaterials() for OBJ/MTL files — when loading the companion .mtl file, tinyobj_loader_c.h calls fopen directly (tinyobj_parse_and_index_mtl_file) and was not covered by the previous patch
• Any future file-loading code (new formats, new decoders) — automatically covered with no extra changes needed
• __wrap_fopen is cleaner than the old android_fopen without the #undef / #define trick.

Testing

Tested on Android with:

• LoadMusicStream (read) for OGG, WAV, and MP3 — loading from APK assets via relative path
• C++ iostream (write) to external storage via absolute path — which in the Android NDK internally uses fopen — confirming third-party code is correctly intercepted

Absolute path write support also benefits from the new fallback added in __wrap_fopen: when internalDataPath/fileName fails, the function now retries with the path as-is, which was previously missing.

[maiconpintoabreu]

Hi @ghera, do not forget the Makefile if ray accepts it.

[raysan5]

@ghera @maiconpintoabreu thanks for the improvement and review, I like the code simplification but I'm a but scary about moving that feature control to the build system instead of keeping it inside code, what about build.zig? what about other custom build systems on user side...

I'm merging it and let's see if it generates further issues on that regards... I also think it should be better documented in the code with some // WARNING: ... messages.