cc/gcc: do not use the core pass-2 to build the baremetal compiler

In case we build a baremetal compiler, use the standard passes:
- core_cc is used to build the C library;
- as such, it is meant to run on build, not host;
- the final compiler is meant to run on host;

As the current final compiler step can not build a baremetal compiler,
call the core backend from the final step.

NB: Currently, newlib is built during the start_files pass, so we have
to have a core compiler by then... Once we can build the baremetal
compiler from the final cc step, then we can move the newlib build to
the proper step, and then get rid of the core pass-1 static compiler...

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

Original patch from: gentoo/src/patchsets/glibc/2.9/6017_all_alpha-glibc-2.8-creat.patch

-= BEGIN original header =-

alpha does not have a __NR_creat

http://bugs.gentoo.org/227275

http://sourceware.org/bugzilla/show_bug.cgi?id=6650

-= END original header =-

diff -durN glibc-2_9.orig/sysdeps/unix/sysv/linux/wordsize-64/creat64.c glibc-2_9/sysdeps/unix/sysv/linux/wordsize-64/creat64.c

--- glibc-2_9.orig/sysdeps/unix/sysv/linux/wordsize-64/creat64.c	2007-11-10 20:34:26.000000000 +0100

+++ glibc-2_9/sysdeps/unix/sysv/linux/wordsize-64/creat64.c	2009-02-02 22:01:35.000000000 +0100

@@ -1 +1,5 @@

 /* Defined as alias for the syscall.  */

+#include <sysdep.h>

+#ifndef __NR_creat

+#include "../../../../../io/creat64.c"

+#endif