Move //lib/DEFS to //tools/DEFS

The macro rules this file defines have nothing to do with the
third-party dependency libraries, but instead are global definitions
used throughout the Gerrit build process. Most build tools are
hidden under //tools, so move these definitions to that directory.

Change-Id: I5e95d7cef734228ca818428a266afc0ac9fa0385

.buckconfig

@@ -8,7 +8,7 @@
   release = //:release
 
 [buildfile]
-  includes = //lib/DEFS
+  includes = //tools/DEFS
 
 [java]
   src_roots = java, resources