cc/gcc: add the backend/frontend infra for final gcc

Currently, we issue the bare-metal compiler from the pass_1 & pass_2
core compilers, because the final gcc breaks while doing so.

This implies we have to build some libces during the start_files step,
instead of the standard libc step. This is the case for newlib.

By adding a backend/frontend infra to the final gcc, we can abstract
what backend to call: the standard backend for non-bare-metal gcc,
and the core backend for bare-metal.

This patch is just an no-op, it just adds the final backend and
frontend without changing the way bare-metal is built, to come in a
subsequent patch.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

alpha does not have a __NR_creat

http://bugs.gentoo.org/227275

http://sourceware.org/bugzilla/show_bug.cgi?id=6650

diff -durN glibc-2.13.orig/sysdeps/unix/sysv/linux/wordsize-64/creat64.c glibc-2.13/sysdeps/unix/sysv/linux/wordsize-64/creat64.c

--- glibc-2.13.orig/sysdeps/unix/sysv/linux/wordsize-64/creat64.c	2007-11-10 20:34:26.000000000 +0100

+++ glibc-2.13/sysdeps/unix/sysv/linux/wordsize-64/creat64.c	2009-11-13 00:50:51.000000000 +0100

@@ -1 +1,5 @@

 /* Defined as alias for the syscall.  */

+#include <sysdep.h>

+#ifndef __NR_creat

+#include "../../../../../io/creat64.c"

+#endif