When compiling on macOS (at least in version 10.12) the TCC compiler failed
to compile libtcc1.a. Three problems were solved:
- The predefined macro "__APPLE__" is now available, as it is tested in the
libc darwin header files
- the libtcc1 Makefile defined _ANSI_SOURCE, although it used signals
- stdargs.h defined va_list differently from the darwin libc.
If the darwin standard library was included BEFORE stdargs this caused
problems.
- the darwin libc generated a warning if GCC < 4 was used
- additional defines are predefined now to make darwin libc headers compile.