Pull in r263301 from upstream llvm trunk (by Ahmed Bougacha):

[AArch64] Don't blindly lower f16/f128 FCCMPs.

Instead, extend f16 (like we do when lowering a standalone SETCC),
and let f128 be legalized to the RT calls.

Fixes PR26803.

This fixes a fatal "Cannot select" backend error when building the
net/freerdp port for AArch64.

PR: 214380
MFC after: 3 days