kbuild: Fix build with binutils <= 2.19

The D option of ar is only available in newer versions.

Signed-off-by: Michal Marek <mmarek@suse.cz>
diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index ed2773e..fae2d8d 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -141,6 +141,11 @@
 ld-option = $(call try-run,\
 	$(CC) /dev/null -c -o "$$TMPO" ; $(LD) $(1) "$$TMPO" -o "$$TMP",$(1),$(2))
 
+# ar-option
+# Usage: KBUILD_ARFLAGS := $(call ar-option,D)
+# Important: no spaces around options
+ar-option = $(call try-run, $(AR) rc$(1) "$$TMP",$(1),$(2))
+
 ######
 
 ###