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>

Original patch from: ../crosstool-NG/ct-ng.trunk/patches/binutils/2.19/160-use-new-ld-dtags.patch

-= BEGIN original header =-

Original patch from Gentoo:

gentoo/src/patchsets/binutils/2.19/76_all_use-new-ld-dtags.patch

-= END original header =-

diff -durN binutils-2.19.1.orig/ld/ldmain.c binutils-2.19.1/ld/ldmain.c

--- binutils-2.19.1.orig/ld/ldmain.c	2009-03-08 11:57:03.000000000 +0100

+++ binutils-2.19.1/ld/ldmain.c	2009-03-08 11:57:03.000000000 +0100

@@ -262,6 +262,7 @@

   link_info.allow_undefined_version = TRUE;

   link_info.keep_memory = TRUE;

+  link_info.new_dtags = TRUE;

   link_info.combreloc = TRUE;

   link_info.strip_discarded = TRUE;

   link_info.emit_hash = TRUE;