[AArch64] Fix save register pairing for Windows AAPCS

Summary:
On Windows, when a function does not have an unwind table (for example, EH
filtering funclets), we don't correctly pair FP and LR to form the frame record
in all circumstances.

Fix this by invalidating a pair when the second register is FP when compiling
for Windows, even when CFI is not needed.

Fixes PR44271 introduced by D65653.

Reviewers: efriedma, sdesmalen, rovka, rengolin, t.p.northover, thegameg, greened

Reviewed By: rengolin

Subscribers: kristof.beyls, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D71754