-Wdeprecated-clean: Fix cases of violating the rule of 5 in ways that are deprecated in C++11

Various targets use std::swap on specific MCAsmOperands (ARM and
possibly Hexagon as well). It might be helpful to mark those subclasses
as final, to ensure that the availability of move/copy operations can't
lead to slicing. (same sort of requirements as the non-vitual dtor -
protected or a final class)

llvm-svn: 243820