Merge r1543187 from trunk:

 * r1543187
   Fix SWIG bindings not building in release mode with out of tree builds.
   Justification:
     Build systems should work.  This makes Branko cranky every release.
   Notes: Test by using ./autogen.sh --release, then do an out of tree build
     without this fix swig-py and swig-rb fail immediately.
   Votes:
     +1: breser, brane, rhuijben


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.8.x@1567520 13f79535-47bb-0310-9956-ffa450edef68