patch 8.2.3067: building fails with Athena

Problem:    Building fails with Athena. (Elimar Riesebieter)
Solution:   Adjust #ifdefs and add the 'drop_file' feature.
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 2539515..d3b2cde 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -4578,6 +4578,13 @@
 		0
 #endif
 		},
+	{"drop_file",
+#ifdef HAVE_DROP_FILE
+		1
+#else
+		0
+#endif
+		},
 	{"emacs_tags",
 #ifdef FEAT_EMACS_TAGS
 		1