linux4.13: another buildfix.

srcpkgs/linux4.13/template

@@ -37,6 +37,9 @@ mutable_files="
  /usr/lib/modules/${_kernver}/modules.devname"
 
 do_configure() {
+	# 4.13rc1 misses Documentation/DocBook. We ship the directory from 4.12 here.
+	cp -a $FILESDIR/DocBook -t Documentation
+
 	# If there's a file called <arch>-dotconfig, use it to
 	# configure the kernel; otherwise use arch defaults and all stuff
 	# as modules (defconfig+allmodconfig).