tools/perf/build: Add feature check core code

Start the split-out of the feature check code by adding a list of features to be
tested, and rules to process that list by building its matching feature-check
file in config/feature-checks/test-<feature>.c.

Add 'hello' as the initial feature.

This structure will allow us to build split-out feature checks in parallel and
thus speed up feature detection dramatically.

No change in functionality: no feature check is used by the build rules yet.

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-pixkihgscFaohfFigq5yt9gs@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

tools/perf/config/Makefile

@@ -89,6 +89,22 @@ CFLAGS += -std=gnu99
 
 EXTLIBS = -lelf -lpthread -lrt -lm -ldl
 
+feature_check = $(eval $(feature_check_code)); $(info CHK: config/feature-checks/test-$(1))
+define feature_check_code
+  feature-$(2) := $(shell make -C config/feature-checks test-$1 >/dev/null 2>/dev/null && echo 1 || echo 0)
+endef
+
+#
+# Build the feature check binaries in parallel, ignore errors, ignore return value and suppress output:
+#
+$(info Testing features:)
+$(shell make -i -j -C config/feature-checks >/dev/null 2>&1)
+$(info done)
+
+FEATURE_TESTS = hello
+
+$(foreach test,$(FEATURE_TESTS),$(call feature_check,$(test),$(test)))
+
 ifeq ($(call try-cc,$(SOURCE_HELLO),$(CFLAGS) -Werror -fstack-protector-all,-fstack-protector-all),y)
   CFLAGS += -fstack-protector-all
 endif

tools/perf/config/feature-checks/Makefile

@@ -0,0 +1,16 @@
+
+FILES=test-hello
+
+all: $(FILES)
+
+BUILD = $(CC) -o $(OUTPUT)$@ $@.c
+
+###############################
+
+test-hello: test-hello.c
+	$(BUILD)
+
+###############################
+
+clean:
+	rm -f $(FILES)

tools/perf/config/feature-checks/test-hello.c

@@ -0,0 +1,6 @@
+#include <stdio.h>
+
+int main(void)
+{
+	return puts("hi");
+}