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>

--- gcc-4.1.0/libstdc++-v3/include/ext/rope.mps	2006-03-24 01:49:51 +0100

+++ gcc-4.1.0/libstdc++-v3/include/ext/rope	2006-03-24 01:49:37 +0100

@@ -59,6 +59,9 @@

 #include <bits/allocator.h>

 #include <ext/hash_fun.h>

+/* cope w/ index defined as macro, SuSv3 proposal */

+#undef index

+

 # ifdef __GC

 #   define __GC_CONST const

 # else

--- gcc-4.1.0/libstdc++-v3/include/ext/ropeimpl.h.mps	2006-03-24 01:50:04 +0100

+++ gcc-4.1.0/libstdc++-v3/include/ext/ropeimpl.h	2006-03-24 01:50:28 +0100

@@ -53,6 +53,9 @@

 #include <ext/memory> // For uninitialized_copy_n

 #include <ext/numeric> // For power

+/* cope w/ index defined as macro, SuSv3 proposal */

+#undef index

+

 _GLIBCXX_BEGIN_NAMESPACE(__gnu_cxx)

   using std::size_t;