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>

 diff -dur strace-4.5.16.orig/configure.ac strace-4.5.16/configure.ac

 --- strace-4.5.16.orig/configure.ac	2007-07-14 19:25:25.000000000 +0200

 +++ strace-4.5.16/configure.ac	2007-07-14 19:27:35.000000000 +0200

 @@ -91,14 +91,14 @@

  	arch=hppa

  	AC_DEFINE([HPPA], 1, [Define for the HPPA architecture.])

  	;;

 -sh)

 -	arch=sh

 -	AC_DEFINE([SH], 1, [Define for the SH architecture.])

 -	;;

  sh64)

  	arch=sh64

  	AC_DEFINE([SH64], 1, [Define for the SH64 architecture.])

  	;;

 +sh*)

 +	arch=sh

 +	AC_DEFINE([SH], 1, [Define for the SH architecture.])

 +	;;

  x86?64*)

  	arch=x86_64

  	AC_DEFINE([X86_64], 1, [Define for the AMD x86-64 architecture.])