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>

Enable using a shell other than bash.

Courtesy "Martin Guy" <martinwguy@yahoo.it>

http://sourceware.org/ml/crossgcc/2008-08/msg00037.html

--- binutils-2.18.orig/ld/genscripts.sh	2007-08-12 20:00:07.000000000 +0100

+++ binutils-2.18/ld/genscripts.sh	2008-08-25 16:09:54.000000000 +0100

@@ -398,9 +398,11 @@

     . $em_script

     em_script=$current_script

   }

-  fragment()

+  

+  alias fragment='em_lineno=$LINENO; fragment_em'

+  fragment_em()

   {

-    local lineno=$[${BASH_LINENO[0]} + 1]

+    local lineno=$[$em_lineno + 1]

     echo >> e${EMULATION_NAME}.c "#line $lineno \"$em_script\""

     cat >> e${EMULATION_NAME}.c

   }