Propagate flags to SDValue in SplitVecOp_VECREDUCE

 This patch is a fix for PR36642.

 While legalizing long vector types, make sure the smaller types get the
 flags of the wider type.

 bugzilla link: https://bugs.llvm.org/show_bug.cgi?id=36642

Change-Id: I0c2829639f094c862c10a6b51b342d4c2563e1fa
llvm-svn: 327079