tools/perf/build: Split out feature check: 'libelf'

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-qznhihaasbysfqO7ffvRsf9q@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/tools/perf/config/Makefile b/tools/perf/config/Makefile
index a2e0e1b2..6865428 100644
--- a/tools/perf/config/Makefile
+++ b/tools/perf/config/Makefile
@@ -108,6 +108,7 @@
 	volatile-register-var		\
 	fortify-source			\
 	bionic				\
+	libelf				\
 	libnuma
 
 $(foreach test,$(FEATURE_TESTS),$(call feature_check,$(test),$(test)))
@@ -164,8 +165,7 @@
   NO_DEMANGLE := 1
   NO_LIBUNWIND := 1
 else
-  FLAGS_LIBELF=$(CFLAGS) $(LDFLAGS) $(EXTLIBS)
-  ifneq ($(call try-cc,$(SOURCE_LIBELF),$(FLAGS_LIBELF),libelf),y)
+  ifeq ($(feature-libelf), 0)
     FLAGS_GLIBC=$(CFLAGS) $(LDFLAGS)
     ifeq ($(call try-cc,$(SOURCE_GLIBC),$(FLAGS_GLIBC),glibc),y)
       LIBC_SUPPORT := 1