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.