patch 8.1.1104: MS-Windows: not all environment variables can be used

Problem:    MS-Windows: not all environment variables can be used.
Solution:   Use the wide version of WinMain() and main(). (Ken Takata,
            closes #4206)
diff --git a/src/main.c b/src/main.c
index 3041df9..a07ce1b 100644
--- a/src/main.c
+++ b/src/main.c
@@ -96,7 +96,7 @@
 static int has_dash_c_arg = FALSE;
 
     int
-# ifdef FEAT_GUI_MSWIN
+# ifdef MSWIN
 #  ifdef __BORLANDC__
 _cdecl
 #  endif