Support arbitrary address space pointers in masked gather/scatter intrinsics.

Fixes PR31789 - When loop-vectorize tries to use these intrinsics for a
non-default address space pointer we fail with a "Calling a function with a
bad singature!" assertion. This patch solves this by adding the 'vector of
pointers' argument as an overloaded type which will determine the address
space.

Differential revision: https://reviews.llvm.org/D31490

llvm-svn: 302018