lib/berkeley-db-1.xx: Add Berkeley DB 1.85 as a submodule.

From https://github.com/pfalcon/berkeley-db-1.xx, which so far contains
pristine 1.85, but will get patches and compile warning fixes going
forward.

Berkeley DB 1.xx is BSD-licensed, and will form the basis of "btree"
simple database module.

.gitmodules

@@ -8,3 +8,6 @@
 [submodule "lib/lwip"]
 	path = lib/lwip
 	url = http://git.savannah.gnu.org/r/lwip.git
+[submodule "lib/berkeley-db-1.xx"]
+	path = lib/berkeley-db-1.xx
+	url = https://github.com/pfalcon/berkeley-db-1.xx

lib/berkeley-db-1.xx

@@ -0,0 +1 @@
+Subproject commit 6dc9d673a4a536341b5ba770809b8e1603819497