tools: Get only verbose output with V=1

Fix having verbose build with V=0, e.g:

 make V=0 -C tools/ perf

Signed-off-by: Robert Richter <robert.richter@calxeda.com>
Link: http://lkml.kernel.org/r/20130503134953.GU8356@rric.localhost


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>