[SelectionDAG] Clamp stack alignment for memset, memmove

memcpy has clamped dst stack alignment to NaturalStackAlignment if
hasStackRealignment is false. We should also clamp stack alignment
for memset and memmove. If we don't clamp, SelectionDAG may first
do tail call optimization which requires no stack realignment. Then
memmove, memset in same function may be lowered to load/store with
larger alignment leading to PEI emit stack realignment code which
is absolutely not correct.

Reviewed By: LuoYuanke

Differential Revision: https://reviews.llvm.org/D136456