patch 8.1.1990: cannot build with eval but without cscope

Problem:    Cannot build with eval but without cscope.
Solution:   Always include if_cscope.pro.
diff --git a/src/version.c b/src/version.c
index 996c85b..e7fd1cf 100644
--- a/src/version.c
+++ b/src/version.c
@@ -758,6 +758,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1990,
+/**/
     1989,
 /**/
     1988,