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-2.12.1/sysdeps/unix/sysv/linux/kernel-features.h	2010-07-27 14:34:39.000000000 +0300

 +++ glibc-2.12.1/sysdeps/unix/sysv/linux/kernel-features.h.new	2011-03-10 18:54:37.686795979 +0200

 @@ -437,7 +437,8 @@

     the code.  On PPC they were introduced in 2.6.17-rc1,

     on SH in 2.6.19-rc1.  */

  #if __LINUX_KERNEL_VERSION >= 0x020611 \

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

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

 +    && (!defined __alpha__)

  # define __ASSUME_ATFCTS	1

  #endif