kbuild: move archive command to scripts/Makefile.lib

scripts/Makefile.build and arch/s390/boot/Makefile use the same
command (thin archiving with symbol table creation).

Avoid the code duplication, and move it to scripts/Makefile.lib.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 850b611..2554a15 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -426,13 +426,9 @@
 # Rule to compile a set of .o files into one .a file (with symbol table)
 #
 ifdef lib-target
-quiet_cmd_link_l_target = AR      $@
-
-# lib target archives do get a symbol table and index
-cmd_link_l_target = rm -f $@; $(AR) rcsTP$(KBUILD_ARFLAGS) $@ $(real-prereqs)
 
 $(lib-target): $(lib-y) FORCE
-	$(call if_changed,link_l_target)
+	$(call if_changed,ar)
 
 targets += $(lib-target)