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>

do not bother running ldconfig on DESTDIR.  it wants to write the temp cache

file outside of the chroot.  doesnt matter anyways as we wont use the cache

results (portage will rebuild cache), so running ldconfig is simply a waste

of time.

diff -durN glibc-2.10.1.orig/Makefile glibc-2.10.1/Makefile

--- glibc-2.10.1.orig/Makefile	2009-04-23 20:23:03.000000000 +0200

+++ glibc-2.10.1/Makefile	2009-11-13 00:49:49.000000000 +0100

@@ -116,6 +116,7 @@

 	rm -f $(symbolic-link-list)

 install:

+dont-bother-with-destdir:

 	-test ! -x $(common-objpfx)elf/ldconfig || LC_ALL=C LANGUAGE=C \

 	  $(common-objpfx)elf/ldconfig $(addprefix -r ,$(install_root)) \

 				       $(slibdir) $(libdir)