patch 8.2.4294: MS-Windows: #ifdefs for Cygwin are too complicated

Problem:    MS-Windows: #ifdefs for Cygwin are too complicated.
Solution:   Simplify the conditions. (Ken Takata, closes #9693)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 71632cd..a584443 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -5196,7 +5196,7 @@
 #endif
 		},
 	{"win32unix",
-#if defined(UNIX) && defined(__CYGWIN__)
+#ifdef WIN32UNIX
 		1
 #else
 		0