perf tools: Fix GNU-only grep usage in Makefile

This makes it work with non-GNU grep's as well.

Signed-off-by: John Spencer <maillist-linux@barfooze.de>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Link: http://thread.gmane.org/gmane.linux.kernel.perf.user/1686
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/config/utilities.mak

@@ -132,7 +132,7 @@ endef
 #
 # Usage: bool-value = $(call is-absolute,path)
 #
-is-absolute = $(shell echo $(shell-sq) | grep ^/ -q && echo y)
+is-absolute = $(shell echo $(shell-sq) | grep -q ^/ && echo y)
 
 # lookup
 #