patch 8.2.3620: memory leak reported in libtlib

Problem:    Memory leak reported in libtlib.
Solution:   Call del_curterm() when cleaning up memory.  Rename term.h to
            termdefs.h to avoid a name clash.
diff --git a/src/config.h.in b/src/config.h.in
index 61b8b76..20339de 100644
--- a/src/config.h.in
+++ b/src/config.h.in
@@ -27,6 +27,9 @@
 /* Define when termcap.h defines outfuntype */
 #undef HAVE_OUTFUNTYPE
 
+/* Define when del_curterm() is available */
+#undef HAVE_DEL_CURTERM
+
 /* Define when __DATE__ " " __TIME__ can be used */
 #undef HAVE_DATE_TIME