Support inline asm with multiple 64bit output in 32bit GPR

Summary: Extend fix for PR34170 to support inline assembly with multiple output operands that do not naturally go in the register class it is constrained to (eg. double in a 32-bit GPR as in the PR).

Reviewers: bogner, t.p.northover, lattner, javed.absar, efriedma

Reviewed By: efriedma

Subscribers: efriedma, tra, eraman, javed.absar, llvm-commits

Differential Revision: https://reviews.llvm.org/D45437

llvm-svn: 339225