Commute the internal flag on MachineOperands.

When commuting a thumb instruction in the size reduction pass, thumb
instructions are represented as a bundle and so some operands may be marked
as internal.  The internal flag has to move with the operand when commuting.

This test is sensitive to register allocation so can't specifically check that
this error was happening, but so long as it continues to pass with -verify then
hopefully its still ok.

rdar://problem/20752113

llvm-svn: 236282