patch 8.0.0531: test with long directory name fails on non-unix systems

Problem:    Test with long directory name fails on non-unix systems.
Solution:   Skip the test on non-unix systems.
diff --git a/src/version.c b/src/version.c
index 16ebc87..56ff4f6 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    531,
+/**/
     530,
 /**/
     529,