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 -durN gcc-4.4.0.orig/libgomp/configure gcc-4.4.0/libgomp/configure

 --- gcc-4.4.0.orig/libgomp/configure	2009-04-21 11:08:08.000000000 +0200

 +++ gcc-4.4.0/libgomp/configure	2009-05-27 21:38:19.000000000 +0200

 @@ -3334,7 +3334,7 @@

  # Add -Wall -Werror if we are using GCC.

  if test "x$GCC" = "xyes"; then

 -  XCFLAGS="$XCFLAGS -Wall -Werror"

 +  XCFLAGS="$XCFLAGS -Wall"

  fi

  # Find other programs we need.