Add rules to generate pre-processed files (just like are available for
the normal kernel build), and adjust the rule to create assembly files
from C ones to produce its output in the output directory rather than
in the source tree.

E.g.

  $ make -C tools/perf/ O=/tmp/perf /tmp/perf/builtin-top.i
  make: Entering directory `/home/git/linux/tools/perf'
      CC /tmp/perf/builtin-top.i
  make: Leaving directory `/home/git/linux/tools/perf'
  $ wc -l /tmp/perf/builtin-top.i
  31379 /tmp/perf/builtin-top.i
  $

Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/4F588A0802000078000770FF@nat28.tlf.novell.comSigned-off-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>