remove legacy i386 fallback stdarg implementation and framework

this has been slated for removal for a long time. there is
fundamentally no way to implement stdarg without compiler assistance;
any attempt to do so has serious undefined behavior; its working
depends not just (as a common misconception goes) on ABI, but also on
assumptions about compiler code generation internal to a translation
unit, which is not subject to external ABI constraints.

include/stdarg.h

@@ -9,14 +9,10 @@ extern "C" {
 
 #include <bits/alltypes.h>
 
-#if __GNUC__ >= 3
 #define va_start(v,l)   __builtin_va_start(v,l)
 #define va_end(v)       __builtin_va_end(v)
 #define va_arg(v,l)     __builtin_va_arg(v,l)
 #define va_copy(d,s)    __builtin_va_copy(d,s)
-#else
-#include <bits/stdarg.h>
-#endif
 
 #ifdef __cplusplus
 }