If a general reduction kernel lacks a combiner function, synthesize one. am: 57fd9f8
am: 2241246

* commit '224124653d24969e95bbe486c135002bcca2b789':
  If a general reduction kernel lacks a combiner function, synthesize one.

Change-Id: Id86999d42f91f9eb424dd9c96d4b9dc557b1cb7a