selftest/vDSO: fix O=

The vDSO selftests ignored the O= or KBUILD_OUTPUT= parameters. Fix it.
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>

tools/testing/selftests/vDSO/Makefile

 # SPDX-License-Identifier: GPL-2.0
+include ../lib.mk
+
 ifndef CROSS_COMPILE
 CFLAGS := -std=gnu99
 CFLAGS_vdso_standalone_test_x86 := -nostdlib -fno-asynchronous-unwind-tables -fno-stack-protector
@@ -6,16 +8,14 @@ ifeq ($(CONFIG_X86_32),y)
 LDLIBS += -lgcc_s
 endif
 
-TEST_PROGS := vdso_test vdso_standalone_test_x86
+TEST_PROGS := $(OUTPUT)/vdso_test $(OUTPUT)/vdso_standalone_test_x86
 
 all: $(TEST_PROGS)
-vdso_test: parse_vdso.c vdso_test.c
-vdso_standalone_test_x86: vdso_standalone_test_x86.c parse_vdso.c
+$(OUTPUT)/vdso_test: parse_vdso.c vdso_test.c
+$(OUTPUT)/vdso_standalone_test_x86: vdso_standalone_test_x86.c parse_vdso.c
 	$(CC) $(CFLAGS) $(CFLAGS_vdso_standalone_test_x86) \
 		vdso_standalone_test_x86.c parse_vdso.c \
-		-o vdso_standalone_test_x86
+		-o $@
 
-include ../lib.mk
-clean:
-	rm -fr $(TEST_PROGS)
+EXTRA_CLEAN := $(TEST_PROGS)
 endif