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>

 # This file declares functions for bare metal kernel (IE. none)

 # Copyright 2008 Yann E. MORIN

 # Licensed under the GPL v2. See COPYING in the root of this package

 CT_DoKernelTupleValues() {

     # For bare-metal, there is no kernel part in the tuple

     CT_TARGET_KERNEL=

 }

 do_kernel_get() {

     :

 }

 do_kernel_extract() {

     :

 }

 do_kernel_headers() {

     :

 }