[PATCH] Fix for PR18921.

[Tim Northover]

  Hi Stepan,

  I don't think the changes to the .td files are needed: basically there's no way for the parser to create a GPRPair operand so the definitions will never trigger.

  If I completely remove your changes to .td files, your tests still pass.

  If you are convinced, could I ask you to remove the existing LDRD GNU hacks from the .td while you're there?

  Cheers.

  Tim

http://llvm-reviews.chandlerc.com/D3277