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>

 diff -durN glibc-2.6.1.orig/glibc-ports-2.6.1/sysdeps/unix/sysv/linux/arm/nptl/sysdep-cancel.h glibc-2.6.1/glibc-ports-2.6.1/sysdeps/unix/sysv/linux/arm/nptl/sysdep-cancel.h

 --- glibc-2.6.1.orig/glibc-ports-2.6.1/sysdeps/unix/sysv/linux/arm/nptl/sysdep-cancel.h	2005-11-16 20:22:59.000000000 +0100

 +++ glibc-2.6.1/glibc-ports-2.6.1/sysdeps/unix/sysv/linux/arm/nptl/sysdep-cancel.h	2007-09-06 13:53:16.000000000 +0200

 @@ -126,3 +126,9 @@

  # define NO_CANCELLATION 1

  #endif

 +

 +#ifndef __ASSEMBLER__

 +# define RTLD_SINGLE_THREAD_P \

 +  __builtin_expect (THREAD_GETMEM (THREAD_SELF, \

 +                   header.multiple_threads) == 0, 1)

 +#endif