selftests: hid: allow to compile hid_bpf with LLVM

clang doesn't like to compile a source to the final binary directly:

clang-14: error: cannot specify -o when generating multiple output files

So split the final rule in 2, and ensure we compile all dependencies
before.

Signed-off-by: Benjamin Tissoires <[e-mail]>
Signed-off-by: Jiri Kosina <[e-mail]>

tools/testing/selftests/hid/Makefile

···
 	$(call msg,MKDIR,,$@)
 	$(Q)mkdir -p $@
 
-$(OUTPUT)/%.o: %.c
-	$(call msg,CC,,$@)
-	$(Q)$(CC) $(CFLAGS) -c $(filter %.c,$^) $(LDLIBS) -o $@
-
 # LLVM's ld.lld doesn't support all the architectures, so use it only on x86
 ifeq ($(SRCARCH),x86)
 LLD := lld
···
 	$(Q)$(BPFTOOL) gen object $(<:.o=.linked1.o) $<
 	$(Q)$(BPFTOOL) gen skeleton $(<:.o=.linked1.o) name $(notdir $(<:.bpf.o=)) > $@
 
-$(OUTPUT)/%:%.c $(BPF_SKELS) $(KHDR_INCLUDES)/linux/hid.h
+$(OUTPUT)/%.o: %.c $(BPF_SKELS) $(KHDR_INCLUDES)/linux/hid.h
+	$(call msg,CC,,$@)
+	$(Q)$(CC) $(CFLAGS) -c $(filter %.c,$^) $(LDLIBS) -o $@
+
+$(OUTPUT)/%: $(OUTPUT)/%.o
 	$(call msg,BINARY,,$@)
 	$(Q)$(LINK.c) $^ $(LDLIBS) -o $@