patch 8.2.2415: no way to check for the cmdwin feature

Problem:    No way to check for the cmdwin feature, cmdline_hist is now always
            enabled.
Solution:   Add has('cmdwin') support. Skip arglist test on Windows
            temporarily.
diff --git a/src/evalfunc.c b/src/evalfunc.c
index cc812ce..b752c51 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -4651,6 +4651,13 @@
 		},
 	{"cmdline_compl", 1},
 	{"cmdline_hist", 1},
+	{"cmdwin",
+#ifdef FEAT_CMDWIN
+		1
+#else
+		0
+#endif
+		},
 	{"comments", 1},
 	{"conceal",
 #ifdef FEAT_CONCEAL