[X86] Stop X86DomainReassignment from creating copies between GR8/GR16...

[X86] Stop X86DomainReassignment from creating copies between GR8/GR16 physical registers and k-registers.

We can only copy between a k-register and a GR32/GR64 register.

This patch detects that the copy will be illegal and prevents the domain reassignment from happening for that closure.

This probably isn't the best fix, and we should probably figure out how to handle this correctly.

Fixes PR38803.

llvm-svn: 343443