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>

 diff -urN uClibc-dist/libc/sysdeps/linux/common/bits/uClibc_touplow.h uClibc/libc/sysdeps/linux/common/bits/uClibc_touplow.h

 --- uClibc-dist/libc/sysdeps/linux/common/bits/uClibc_touplow.h   Fri Jun  3 13:30:25 2005

 +++ uClibc/libc/sysdeps/linux/common/bits/uClibc_touplow.h   Fri Jun  3 13:30:39 2005

 @@ -34,11 +34,11 @@

  /* glibc uses the equivalent of - typedef __int32_t __ctype_touplow_t; */

 -typedef __uint16_t __ctype_mask_t;

 +typedef __uint32_t __ctype_mask_t;

  #ifdef __UCLIBC_HAS_CTYPE_SIGNED__

 -typedef __int16_t __ctype_touplow_t;

 +typedef __int32_t __ctype_touplow_t;

  #define __UCLIBC_CTYPE_B_TBL_OFFSET       128

  #define __UCLIBC_CTYPE_TO_TBL_OFFSET      128