tools/perf/build: Remove the volatile-register-var feature check

Namhyung Kim noticed that the volatile-register-var feature check
is superfluous:

 > The gcc manpage says this warning is enabled by -Wall, and we add -Wall
 > to CFLAGS before doing feature checks.  So all gcc versions that support
 > -Wvolatile-register-var enables it by default without this check and
 > older gcc versions will always fail the feature check.

Remove it - this will further speed up feature checks.
Reported-by: Namhyung Kim <namhyung@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/config/Makefile

@@ -132,8 +132,7 @@ CORE_FEATURE_TESTS =			\
 	libunwind			\
 	on-exit				\
 	stackprotector			\
-	stackprotector-all		\
-	volatile-register-var
+	stackprotector-all
 
 #
 # So here we detect whether test-all was rebuilt, to be able
@@ -203,10 +202,6 @@ ifeq ($(feature-stackprotector), 1)
   CFLAGS += -Wstack-protector
 endif
 
-ifeq ($(feature-volatile-register-var), 1)
-  CFLAGS += -Wvolatile-register-var
-endif
-
 ifeq ($(DEBUG),0)
   ifeq ($(feature-fortify-source), 1)
     CFLAGS += -D_FORTIFY_SOURCE=2

tools/perf/config/feature-checks/Makefile

@@ -25,8 +25,7 @@ FILES=					\
 	test-libunwind			\
 	test-on-exit			\
 	test-stackprotector-all		\
-	test-stackprotector		\
-	test-volatile-register-var
+	test-stackprotector
 
 CC := $(CC) -MD
 
@@ -37,7 +36,7 @@ BUILD = $(CC) $(LDFLAGS) -o $(OUTPUT)$@ $@.c
 ###############################
 
 test-all:
-	$(BUILD) -Werror -fstack-protector -fstack-protector-all -Wvolatile-register-var -O2 -Werror -D_FORTIFY_SOURCE=2 -ldw -lelf -lnuma -lunwind -lunwind-x86_64 -lelf -laudit -I/usr/include/slang -lslang $(shell pkg-config --libs --cflags gtk+-2.0 2>/dev/null) $(FLAGS_PERL_EMBED) $(FLAGS_PYTHON_EMBED) -DPACKAGE='"perf"' -lbfd -ldl
+	$(BUILD) -Werror -fstack-protector -fstack-protector-all -O2 -Werror -D_FORTIFY_SOURCE=2 -ldw -lelf -lnuma -lunwind -lunwind-x86_64 -lelf -laudit -I/usr/include/slang -lslang $(shell pkg-config --libs --cflags gtk+-2.0 2>/dev/null) $(FLAGS_PERL_EMBED) $(FLAGS_PYTHON_EMBED) -DPACKAGE='"perf"' -lbfd -ldl
 
 test-hello:
 	$(BUILD)
@@ -48,9 +47,6 @@ test-stackprotector-all:
 test-stackprotector:
 	$(BUILD) -Werror -fstack-protector
 
-test-volatile-register-var:
-	$(BUILD) -Werror -Wvolatile-register-var
-
 test-fortify-source:
 	$(BUILD) -O2 -Werror -D_FORTIFY_SOURCE=2