libc/newlib: build newlib in the proper step

Currently, newlib is built in the start_file step, which is wrong, but was
needed when the baremetal integration was... well, 'unfinished'.

Now that we build the baremetal compiler from the final cc step, and a
proper core gcc in pass-1 and pass-2, we can move the newlib build to the
step do_libc, where it belongs.

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

 diff -ru gdb-6.8.orig/bfd/sysdep.h gdb-6.8/bfd/sysdep.h

 --- gdb-6.8.orig/bfd/sysdep.h	2007-07-03 16:26:42.000000000 +0200

 +++ gdb-6.8/bfd/sysdep.h	2011-08-21 13:33:47.000000000 +0200

 @@ -131,7 +131,7 @@

  extern PTR realloc ();

  #endif

 -#if !HAVE_DECL_STPCPY

 +#if !HAVE_DECL_STPCPY && !defined(stpcpy)

  extern char *stpcpy (char *__dest, const char *__src);

  #endif