GlobalISel: Ignore callsite attributes when picking intrinsic type

A target intrinsic may be defined as possibly reading memory, but the
call site may have additional knowledge that it doesn't read
memory. The intrinsic lowering will expect the pessimistic assumption
of the intrinsic definition, so the chain should still be used.

I fixed the same bug in SelectionDAG in r287593.

llvm-svn: 363580