flex fails to cross build from source with gcc-15. During a cross build,
the file lib/malloc.c is compiled. This does not happen during native
builds, which is why native builds are unaffected. In any case, this
file declares

    void *malloc();

and while gcc <= 14 interpret this as the arguments being unknown,
gcc >= 15 understands this as no arguments. Now when rpl_malloc calls
malloc(n), gcc >= 15 is very unhappy as it only expected 0 arguments.

This function is never used during builds on and for glibc, but it still
makes the build fail. I propose declaring the correct function
prototype.

Helmut