Import various libgcc functions from syslinux.

Experimentation reveals that gcc ignores -mrtd for the implicit
arithmetic functions (e.g. __udivdi3), but not for the implicit
memcpy() and memset() functions.  Mark the implicit arithmetic
functions with __attribute__((cdecl)) to compensate for this.

(Note: we cannot mark with with __cdecl, because we define __cdecl to
incorporate regparm(0) as well.)

src/core/gcc_implicit.c

@@ -1,20 +0,0 @@
-/** @file
- *
- * gcc implicit functions
- *
- * gcc sometimes likes to insert implicit calls to memcpy().
- * Unfortunately, there doesn't seem to be any way to prevent it from
- * doing this, or to force it to use the optimised memcpy() as seen by
- * C code; it insists on inserting a symbol reference to "memcpy".  We
- * therefore include wrapper functions just to keep gcc happy.
- *
- */
-
-#include <string.h>
-
-void * gcc_implicit_memcpy ( void *dest, const void *src,
-			     size_t len ) asm ( "memcpy" );
-
-void * gcc_implicit_memcpy ( void *dest, const void *src, size_t len ) {
-	return memcpy ( dest, src, len );
-}