Add redundant dependency from verify tests to //hphp/hhvm:hhvm_link

Summary:
I removed this edge in D6969411 because nothing in our tests directly
uses its output, but it turns out we want our test targets to be artifically
close to the rest of HHVM (see https://fburl.com/3dpob2w2).

Reviewed By: ricklavoie, markw65

Differential Revision: D6992943

fbshipit-source-id: aa6166b2d135f23c2829ce90de809163840126b5

hphp/test/DEFS

@@ -50,6 +50,17 @@ def verify_unittest(suite, repo, dir, mode='interp,jit',
 
   deplist=[
     '//hphp/hhvm:hhvm',
+    # This dependency on hhvm_link shouldn't be necessary, since hhvm already
+    # depends (indirectly) on hhvm_link. But we have it here for two reasons:
+    #
+    # 1) Our test targets need to be within 6 dependency hops of all of our
+    #    source files (see https://fburl.com/3dpob2w2).
+    #
+    # 2) In a dev build, when Buck gets the hhvm binary from cache, it doesn't
+    #    build all the necessary .so files (this is an issue with hhvm:hhvm
+    #    being a custom_rule). A direct dependency on hhvm_link forces Buck to
+    #    build them.
+    '//hphp/hhvm:hhvm_link',
     '//hphp/hhvm:symlinks',
     '//hphp/test:run',
     ('' if dir.startswith('//') else '//hphp/test:') + dir,