libtcc1: Don't use stdlib functions

libtcc1 is the compiler support library and therefore needs
to function in a freestanding environment.  In particular
it can't just use fprintf or stderr, which it was on x86-64
(but only when compiled by GCC).  The tight integration between
libtcc1 and tcc itself makes it impossible to ever reach that
case so the abort() there is enough.  abort() is strictly speaking
also not available in a freestanding environment, but it often is
nevertheless.

lib/libtcc1.c

@@ -700,9 +700,6 @@ void *__va_arg(__va_list_struct *ap,
         return ap->overflow_arg_area - size;
 
     default: /* should never happen */
-#ifndef __TINYC__
-        fprintf(stderr, "unknown ABI type for __va_arg\n");
-#endif
         abort();
     }
 }