selftests: cgroup: build error multiple outpt files

When building selftests/cgroup: with clang the following error are seen:

clang -Wall -pthread    test_memcontrol.c cgroup_util.c ../clone3/clone3_selftests.h  -o .../builds/current/kselftest/cgroup/test_memcontrol
clang: error: cannot specify -o when generating multiple output files
make[3]: *** [../lib.mk:146: .../builds/current/kselftest/cgroup/test_memcontrol] Error 1

Rework to add the header files to LOCAL_HDRS before including ../lib.mk,
since the dependency is evaluated in '$(OUTPUT)/%:%.c $(LOCAL_HDRS)' in
file lib.mk.
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/cgroup/Makefile

@@ -11,10 +11,12 @@ TEST_GEN_PROGS += test_core
 TEST_GEN_PROGS += test_freezer
 TEST_GEN_PROGS += test_kill
 
+LOCAL_HDRS += $(selfdir)/clone3/clone3_selftests.h $(selfdir)/pidfd/pidfd.h
+
 include ../lib.mk
 
-$(OUTPUT)/test_memcontrol: cgroup_util.c ../clone3/clone3_selftests.h
-$(OUTPUT)/test_kmem: cgroup_util.c ../clone3/clone3_selftests.h
-$(OUTPUT)/test_core: cgroup_util.c ../clone3/clone3_selftests.h
-$(OUTPUT)/test_freezer: cgroup_util.c ../clone3/clone3_selftests.h
-$(OUTPUT)/test_kill: cgroup_util.c ../clone3/clone3_selftests.h ../pidfd/pidfd.h
+$(OUTPUT)/test_memcontrol: cgroup_util.c
+$(OUTPUT)/test_kmem: cgroup_util.c
+$(OUTPUT)/test_core: cgroup_util.c
+$(OUTPUT)/test_freezer: cgroup_util.c
+$(OUTPUT)/test_kill: cgroup_util.c

tools/testing/selftests/lib.mk

@@ -141,7 +141,7 @@ endif
 # Selftest makefiles can override those targets by setting
 # OVERRIDE_TARGETS = 1.
 ifeq ($(OVERRIDE_TARGETS),)
-LOCAL_HDRS := $(selfdir)/kselftest_harness.h $(selfdir)/kselftest.h
+LOCAL_HDRS += $(selfdir)/kselftest_harness.h $(selfdir)/kselftest.h
 $(OUTPUT)/%:%.c $(LOCAL_HDRS)
 	$(LINK.c) $(filter-out $(LOCAL_HDRS),$^) $(LDLIBS) -o $@