3.4 PATCH: Allow building IRIX 6 libgnat

[Rainer Orth]

Richard Kenner writes:

>     -   Functions_Return_By_DSP   : constant Boolean := True;
>     +   Functions_Return_By_DSP   : constant Boolean := False;
> 
> This turns off a pretty important feature.  Rather than do that, I'd
> like to understand what the bug in that feature is.  Do you have any
> further information?

Sure: see PR middle-end/6552 for all the details.

	Rainer