Make the first build set "make linktypes.xml".

linktypes.xml has to be built before we build anything else;
unfortunately, there doesn't seem to be a way to do that in our
Makefile, given the way lib/main.mk works.

.circleci/config.yml

@@ -42,7 +42,9 @@ jobs:
       # Build txt and html versions of drafts
       - run:
           name: "Build Drafts"
-          command: "make 'CLONE_ARGS=--reference ~/git-reference'"
+          command: |
+            make linktypes.xml
+            make 'CLONE_ARGS=--reference ~/git-reference'
 
       # Update editor's copy on gh-pages
       - run: