patch_args: allow use of --directory parameter

patch(1) has a -d/--directory parameter which allows us to specify a directory
where the patch will be applied. This is especially useful when we have
multiple distfiles and want to patch in $build_wrksrc because that's where the
patch is usually applied.

Problem is, that the -i parameter is also relative to the the -d parameter and
thus fails to find the patch, when -d is set. We solve that by using standard
input instead of -i.

common/hooks/do-patch/00-patches.sh

@@ -31,7 +31,7 @@ _process_patch() {
 
 	cd "$wrksrc"
 	msg_normal "$pkgver: patching: ${_patch}.\n"
-	patch -s ${_args} -i ${_patch} 2>/dev/null
+	patch -s ${_args} <${_patch} 2>/dev/null
 }
 
 hook() {