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 building a pure soft-float compiler without the need for a software

floating point library.

diff -dur gcc-4.0.4.orig/gcc/config.gcc gcc-4.0.4/gcc/config.gcc

--- gcc-4.0.4.orig/gcc/config.gcc	2007-02-02 19:12:28.000000000 +0100

+++ gcc-4.0.4/gcc/config.gcc	2007-02-02 19:12:07.000000000 +0100

@@ -677,7 +677,7 @@

 		tm_defines="TARGET_BIG_ENDIAN_DEFAULT=1 $tm_defines"

 		;;

 	esac

-	tmake_file="${tmake_file} arm/t-arm arm/t-linux"

+	tmake_file="${tmake_file} arm/t-arm arm/t-linux arm/t-arm-elf"

 	extra_parts="crtbegin.o crtbeginS.o crtend.o crtendS.o"

 	gnu_ld=yes

 	;;