[rcore][android] Document --wrap=fopen linker flag requirements per build system

[ghera]

Follow-up to #5605, addressing @raysan5's suggestion for // WARNING: comments in code.

Adds a comment block before __real_fopen/__wrap_fopen explaining how and where -Wl,--wrap=fopen must be applied for each supported build system, including the behavioral difference between CMake (flag propagates to final app link) and Make (SHARED) (wraps libraylib.so only).

Tested on CMake and Make (both SHARED and STATIC). For build.zig, several approaches were attempted but none are available in the std.Build API required by raylib (0.16.0-dev.2349+); this will probably change in the near future, but for now the flag must be passed externally in the final link step.

[maiconpintoabreu]

Hi @ghera for zig, can you not just add on the list of flags?

    try raylib_flags_arr.appendSlice(
        b.allocator,
        &[_][]const u8{
            "-std=gnu99",
            "-D_GNU_SOURCE",
                       <--------------------------------------------------------- Here
            "-DGL_SILENCE_DEPRECATION=199309L",
            "-fno-sanitize=undefined", // https://github.com/raysan5/raylib/issues/3674
        },
    );

I do not have the v16 yet so I cannot test it sorry.

[ghera]

@maiconpintoabreu No worries. I hadn’t tried that part earlier because I assumed those were C compiler flags rather than linker flags. I tried using .addLinkerArgs / .addLinkerArg, but none of them seem to work with Zig 0.16.

When I get a chance, I’ll try your suggestion and put together a more detailed report covering the different build scenarios.

[raysan5]

@ghera thanks for the improvement! Definitely helpful for users dealing with custom build systems!

[ghera]

Hi @maiconpintoabreu, I ran the full Android checks for build.zig, and adding -Wl,--wrap=fopen to raylib_flags_arr gives this for libraylib.so:

T __wrap_fopen
U __real_fopen
U fopen@LIBC

while the expected pattern should be T __wrap_fopen + U fopen@LIBC (without U __real_fopen).

So, based on the symbol evidence, it looks like --wrap=fopen is not being applied in Zig, even though it appears in the command line. Practically, it behaves as if that option is ineffective (or applied in the wrong phase) for this workflow.

For static, it remains true that wrapping must be activated at the consumer final link step.

Because of that, the Zig warning seems correct: --wrap should currently be treated as a final-link-step requirement (until std.Build provides a more suitable linker hook / API).

Thanks to your suggestion and the resulting tests, I also found a small issue in the standalone CMake shared build, and I’ll address it in a separate PR. Building libraylib.so standalone is a relatively uncommon workflow for most Android users though.