tools/perf/build: Split out feature check: 'volatile-register-var'

Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/n/tip-5dOevlybbwvbk3zTbcxrrqet@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/tools/perf/config/Makefile b/tools/perf/config/Makefile
index 9f94912..a3de2f8 100644
--- a/tools/perf/config/Makefile
+++ b/tools/perf/config/Makefile
@@ -105,6 +105,7 @@
 	hello				\
 	stackprotector-all		\
 	stackprotector			\
+	volatile-register-var		\
 	libnuma
 
 $(foreach test,$(FEATURE_TESTS),$(call feature_check,$(test),$(test)))
@@ -117,7 +118,7 @@
   CFLAGS += -Wstack-protector
 endif
 
-ifeq ($(call try-cc,$(SOURCE_HELLO),$(CFLAGS) -Werror -Wvolatile-register-var,-Wvolatile-register-var),y)
+ifeq ($(feature-volatile-register-var), 1)
   CFLAGS += -Wvolatile-register-var
 endif