Move jdiff and doclava to be composite build dependencies.

Test: ./gradlew buildOnServer
Change-Id: I39420d22cae3ab082b3f7b005aff246155cebe5a
diff --git a/settings.gradle b/settings.gradle
index c281bb1..63938e7 100644
--- a/settings.gradle
+++ b/settings.gradle
@@ -188,11 +188,9 @@
 
 File externalRoot = new File(rootDir, '../../external')
 
-include ':doclava'
-project(':doclava').projectDir = new File(externalRoot, 'doclava')
+includeBuild new File(externalRoot, 'doclava')
 
-include ':jdiff'
-project(':jdiff').projectDir = new File(externalRoot, 'jdiff')
+includeBuild new File(externalRoot, 'jdiff')
 
 include ':noto-emoji-compat'
 project(':noto-emoji-compat').projectDir = new File(externalRoot, 'noto-fonts/emoji-compat')