cpp/experimental/simd/reduce

@1@ Reduces all values in over. @2@ Reduces the values in where the associated mask element is  over. @3@ Returns the sum of all values in where the associated mask element is. @4@ Returns the product of all values in where the associated mask element is. @5@ Returns the aggregation using bitwise-and of all values in where the associated mask element is. @6@ Returns the aggregation using bitwise-or of all values in where the associated mask element is. @7@ Returns the aggregation using bitwise-xor of all values in where the associated mask element is. @8@ Reduces all values in over. @9@ Reduces all values in where the associated mask element is  over. @10@ Reduces all values in over. @11@ Reduces all values in where the associated mask element is  over.

The behavior is non-deterministic if is not associative or not commutative.