[Patch, Darwin/PPC64] Fix ABI break on long double structs.

[Mike Stump]

On Dec 9, 2010, at 10:29 AM, IainS wrote:
> In the case that we have a structure containing exactly enough long doubles to straddle the split-point (between pass-in-reg and pass-on-stack) we currently get it wrong and believe that we can pass the whole entity in regs.
> 
> Incidentally, the system gcc-4.2.1 is also broken this way (dunno if it's worth filing a radar tho).

Probably not.

> OK for trunk?

Ok.