perf tools: Fix non-debug build

In the absence of s DEBUG variable definition on the command line perf
tools was building without optimization.  Fix by assigning DEBUG if it
is not defined.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1382427258-17495-2-git-send-email-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/config/Makefile

@@ -66,6 +66,10 @@ ifneq ($(WERROR),0)
   CFLAGS += -Werror
 endif
 
+ifndef DEBUG
+  DEBUG := 0
+endif
+
 ifeq ($(DEBUG),0)
   CFLAGS += -O6
 endif