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

* commit '57fd9f882f3359be4201c42b02aebf785d311df2':
  If a general reduction kernel lacks a combiner function, synthesize one.

Change-Id: I3187508fc8d6f2f14b42f9d1ae401a33183d4701