kbuild: Add resolve_btfids clean to root clean target

The resolve_btfids tool is used during the kernel build,
so we should clean it on kernel's make clean.

Invoking the the resolve_btfids clean as part of root
'make clean'.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20210205124020.683286-5-jolsa@kernel.org

Makefile

@@ -1086,6 +1086,11 @@ ifdef CONFIG_STACK_VALIDATION
   endif
 endif
 
+PHONY += resolve_btfids_clean
+
+resolve_btfids_clean:
+	$(Q)$(MAKE) -sC $(srctree)/tools/bpf/resolve_btfids O=$(abspath $(objtree))/tools/bpf/resolve_btfids clean
+
 ifdef CONFIG_BPF
 ifdef CONFIG_DEBUG_INFO_BTF
   ifeq ($(has_libelf),1)
@@ -1495,7 +1500,7 @@ vmlinuxclean:
 	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/link-vmlinux.sh clean
 	$(Q)$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) clean)
 
-clean: archclean vmlinuxclean
+clean: archclean vmlinuxclean resolve_btfids_clean
 
 # mrproper - Delete all generated files, including .config
 #