patch 8.1.0474: directory where if_perl.c is written is inconsistent

Problem:    Directory where if_perl.c is written is inconsistent.
Solution:   use auto/if_perl.c for MS-Windows. (Ken Takata, closes #3540)
diff --git a/src/version.c b/src/version.c
index 995adff..5190030 100644
--- a/src/version.c
+++ b/src/version.c
@@ -793,6 +793,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    474,
+/**/
     473,
 /**/
     472,