This patch enables SimplifyUsingDistributiveLaws() to handle following pattens.

(X >> Z) & (Y >> Z)  -> (X&Y) >> Z  for all shifts.
(X >> Z) | (Y >> Z)  -> (X|Y) >> Z  for all shifts.
(X >> Z) ^ (Y >> Z)  -> (X^Y) >> Z  for all shifts.

These patterns were previously handled separately in visitAnd()/visitOr()/visitXor().

Differential Revision: http://reviews.llvm.org/D4951