perf tools: Add signal.h to places using its definitions

And remove it from util.h, disentangling it a bit more.

Link: http://lkml.kernel.org/n/tip-2zg9s5nx90yde64j3g4z2uhk@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
index fe1dcd4f..76a88bd 100644
--- a/tools/perf/builtin-script.c
+++ b/tools/perf/builtin-script.c
@@ -35,6 +35,7 @@
 #include <dirent.h>
 #include <errno.h>
 #include <inttypes.h>
+#include <signal.h>
 
 #include "sane_ctype.h"