patch 9.1.0670: po file encoding fails on *BSD during make

Problem:  po file encoding fails on *BSD during make
Solution: instead of using `$<` make use of variable `$?` which should
          be equivalent when the rule is dependent on only a single
          file (RestorerZ).

closes: #15471

Signed-off-by: RestorerZ <restorer@mail2k.ru>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/version.c b/src/version.c
index c58e82e..0365833 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    670,
+/**/
     669,
 /**/
     668,