[llvm] r212638 - AArch64: Better codegen for storing to __fp16.

[Tim Northover]

Hi Jim,

> This also eliminates an extra step in the convert-from-f64 path
> which was first converting to f32 and then to f16 from there.

Is that allowed in strict IEEE? We're not allowed to form FMAs
willy-nilly even though they're guaranteed more precise, for example.
I'd have said the original double-conversion issue needed fixing in
Clang.

Cheers.

Tim.