patch 8.2.4316: __CYGWIN32__ is not defined on 64 bit systems

Problem:    __CYGWIN32__ is not defined on 64 bit systems.
Solution:   Update #ifdefs. (Ken Takata, closes #9709)
diff --git a/src/main.c b/src/main.c
index 5d02c95..80cff7c 100644
--- a/src/main.c
+++ b/src/main.c
@@ -2571,7 +2571,7 @@
 		}
 	    }
 #endif
-#ifdef __CYGWIN32__
+#ifdef __CYGWIN__
 	    /*
 	     * If vim is invoked by non-Cygwin tools, convert away any
 	     * DOS paths, so things like .swp files are created correctly.