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>

--- glibc-2.7/sysdeps/unix/sysv/linux/kernel-features.h	2007-08-14 06:21:09.000000000 +0300

+++ glibc-2.7/sysdeps/unix/sysv/linux/kernel-features.h.new	2008-07-23 07:05:20.000000000 +0300

@@ -454,8 +454,7 @@

    and on Alpha just after 2.6.22-rc1.  */

 #if __LINUX_KERNEL_VERSION >= 0x020611 \

     && ((!defined __sh__ && !defined __alpha__) \

-	|| (__LINUX_KERNEL_VERSION >= 0x020613 && defined __sh__) \

-	|| (__LINUX_KERNEL_VERSION >= 0x020617 && defined __alpha__))

+	|| (__LINUX_KERNEL_VERSION >= 0x020613 && defined __sh__))

 # define __ASSUME_ATFCTS	1

 #endif