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 -durN gcc-4.4.0.orig/include/libiberty.h gcc-4.4.0/include/libiberty.h

 --- gcc-4.4.0.orig/include/libiberty.h	2008-06-24 03:42:31.000000000 +0200

 +++ gcc-4.4.0/include/libiberty.h	2009-05-27 21:38:24.000000000 +0200

 @@ -595,8 +595,11 @@

  /* Like sprintf but provides a pointer to malloc'd storage, which must

     be freed by the caller.  */

 +/* asprintf may be declared as a macro by glibc with __USE_FORTIFY_LEVEL.  */

 +#ifndef asprintf

  extern int asprintf (char **, const char *, ...) ATTRIBUTE_PRINTF_2;

  #endif

 +#endif

  #if !HAVE_DECL_VASPRINTF

  /* Like vsprintf but provides a pointer to malloc'd storage, which