selftests: lib.mk: kselftest and kselftest-clean fail for make O=dir case

kselftest and kselftest-clean targets fail when object directory is
specified to relocate objects. Main Makefile make O= path clears the
built-in defines LINK.c, COMPILE.S, LINK.S, and RM that are used in
lib.mk to build and clean targets. Define them.
Signed-off-by: NShuah Khan <shuahkh@osg.samsung.com>

tools/testing/selftests/lib.mk

@@ -7,6 +7,7 @@ OUTPUT := $(shell pwd)
 endif
 
 TEST_GEN_PROGS := $(patsubst %,$(OUTPUT)/%,$(TEST_GEN_PROGS))
+TEST_GEN_PROGS_EXTENDED := $(patsubst %,$(OUTPUT)/%,$(TEST_GEN_PROGS_EXTENDED))
 TEST_GEN_FILES := $(patsubst %,$(OUTPUT)/%,$(TEST_GEN_FILES))
 
 all: $(TEST_GEN_PROGS) $(TEST_GEN_PROGS_EXTENDED) $(TEST_GEN_FILES)
@@ -62,6 +63,11 @@ endef
 emit_tests:
 	$(EMIT_TESTS)
 
+# define if isn't already. It is undefined in make O= case.
+ifeq ($(RM),)
+RM := rm -f
+endif
+
 define CLEAN
 	$(RM) -r $(TEST_GEN_PROGS) $(TEST_GEN_PROGS_EXTENDED) $(TEST_GEN_FILES) $(EXTRA_CLEAN)
 endef
@@ -69,6 +75,15 @@ endef
 clean:
 	$(CLEAN)
 
+# When make O= with kselftest target from main level
+# the following aren't defined.
+#
+ifneq ($(KBUILD_SRC),)
+LINK.c = $(CC) $(CFLAGS) $(CPPFLAGS) $(LDFLAGS) $(TARGET_ARCH)
+COMPILE.S = $(CC) $(ASFLAGS) $(CPPFLAGS) $(TARGET_ARCH) -c
+LINK.S = $(CC) $(ASFLAGS) $(CPPFLAGS) $(LDFLAGS) $(TARGET_ARCH)
+endif
+
 $(OUTPUT)/%:%.c
 	$(LINK.c) $^ $(LDLIBS) -o $@