selftests/bpf: remove generated verifier/tests.h on 'make clean'

'make clean' is supposed to remove generated files.
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Acked-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/Makefile

@@ -216,7 +216,8 @@ ifeq ($(DWARF2BTF),y)
 	$(BTF_PAHOLE) -J $@
 endif
 
-$(OUTPUT)/test_verifier: $(OUTPUT)/verifier/tests.h
+VERIFIER_TESTS_H := $(OUTPUT)/verifier/tests.h
+$(OUTPUT)/test_verifier: $(VERIFIER_TESTS_H)
 $(OUTPUT)/test_verifier: CFLAGS += -I$(OUTPUT)
 
 VERIFIER_TEST_FILES := $(wildcard verifier/*.c)
@@ -227,6 +228,7 @@ $(OUTPUT)/verifier/tests.h: $(VERIFIER_TEST_FILES)
 		  ls *.c 2> /dev/null | \
 			sed -e 's@\(.*\)@#include \"\1\"@'; \
 		  echo '#endif' \
-		 ) > $(OUTPUT)/verifier/tests.h)
+		 ) > $(VERIFIER_TESTS_H))
 
-EXTRA_CLEAN := $(TEST_CUSTOM_PROGS) $(ALU32_BUILD_DIR)
+EXTRA_CLEAN := $(TEST_CUSTOM_PROGS) $(ALU32_BUILD_DIR) \
+	$(VERIFIER_TESTS_H)