patch 8.1.2361: MS-Windows: test failures related to VIMDLL

Problem:    MS-Windows: test failures related to VIMDLL.
Solution:   Adjust code and tests. (Ken Takata, closes #5283)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 254b2a9..a071ad8 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -3355,7 +3355,7 @@
 #ifdef FEAT_SEARCHPATH
 	"file_in_path",
 #endif
-#ifdef FEAT_FILTERPIPE
+#if defined(FEAT_FILTERPIPE) && !defined(VIMDLL)
 	"filterpipe",
 #endif
 #ifdef FEAT_FIND_ID
@@ -3819,6 +3819,10 @@
 	else if (STRICMP(name, "clipboard_working") == 0)
 	    n = clip_star.available;
 #endif
+#ifdef VIMDLL
+	else if (STRICMP(name, "filterpipe") == 0)
+	    n = gui.in_use || gui.starting;
+#endif
     }
 
     rettv->vval.v_number = n;