On my system (Mac OS 10.6) /usr/include/stdarg.h is:
/* This file is public domain. */
/* GCC uses its own copy of this header */
#if defined(__GNUC__)
#include_next <stdarg.h>
#elif defined(__MWERKS__)
#include "mw_stdarg.h"
#else
#error "This header only supports __MWERKS__."
#endif
So, if GCC uses its own copy of stdarg.h, where is it? I have no idea on what
that #include_next means (maybe a GCC extension?), nor something about
"MWERKS" (a compiler?).