objtool: make it visible in make V=1 output

It is currently impossible to see what is going on with objtool when
building, so call echo-cmd to see the actions:
  gcc -Wp,-MD,arch/x86/entry/.entry_64.o.d  -nostdinc -isystem ...
  ./tools/objtool/objtool check "arch/x86/entry/entry_64.o";
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Michal Marek <mmarek@suse.com>
Cc: linux-kbuild@vger.kernel.org
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

scripts/Makefile.build

@@ -280,14 +280,14 @@ define rule_cc_o_c
 	$(call echo-cmd,checksrc) $(cmd_checksrc)			  \
 	$(call cmd_and_fixdep,cc_o_c)					  \
 	$(cmd_modversions_c)						  \
-	$(cmd_objtool)						          \
+	$(call echo-cmd,objtool) $(cmd_objtool)				  \
 	$(call echo-cmd,record_mcount) $(cmd_record_mcount)
 endef
 
 define rule_as_o_S
 	$(call cmd_and_fixdep,as_o_S)					  \
 	$(cmd_modversions_S)						  \
-	$(cmd_objtool)
+	$(call echo-cmd,objtool) $(cmd_objtool)
 endef
 
 # List module undefined symbols (or empty line if not enabled)