[TargetLowering] Add MachineMemOperand::Flags to allowsMemoryAccess tests (PR42123)

[TargetLowering] Add MachineMemOperand::Flags to allowsMemoryAccess tests (PR42123)

As discussed on D62910, we need to check whether particular types of memory access are allowed, not just their alignment/address-space.

This NFC patch adds a MachineMemOperand::Flags argument to allowsMemoryAccess and allowsMisalignedMemoryAccesses, and wires up calls to pass the relevant flags to them.

If people are happy with this approach I can then update X86TargetLowering::allowsMisalignedMemoryAccesses to handle misaligned NT load/stores.

Differential Revision: https://reviews.llvm.org/D63075

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@363179 91177308-0d34-0410-b5e6-96231b3b80d8