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 Gentoo.

-= BEGIN original header =-

-= END original header =-

diff -durN uClibc-0.9.30.orig/libc/inet/resolv.c uClibc-0.9.30/libc/inet/resolv.c

--- uClibc-0.9.30.orig/libc/inet/resolv.c	2008-11-02 01:25:33.000000000 +0100

+++ uClibc-0.9.30/libc/inet/resolv.c	2009-02-07 09:57:59.000000000 +0100

@@ -1788,7 +1788,7 @@

 int gethostent_r(struct hostent *result_buf, char *buf, size_t buflen,

 	struct hostent **result, int *h_errnop)

 {

-	int ret;

+	int ret = HOST_NOT_FOUND;

 	__UCLIBC_MUTEX_LOCK(mylock);

 	if (__gethostent_fp == NULL) {