patch 8.2.1981: MinGW: parallel compilation might fail

Problem:    MinGW: parallel compilation might fail.
Solution:   Add dependencies on $(OUTDIR). (Masamichi Abe, closes #7287)
diff --git a/src/version.c b/src/version.c
index d1e174d..3dde5b2 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1981,
+/**/
     1980,
 /**/
     1979,