Remove obsolete Tru64 UNIX V5.1B support

[Jakub Jelinek]

On Mon, Mar 05, 2012 at 09:28:18AM -0800, Richard Henderson wrote:
> >   TARGET_HAS_XFLOATING_LIBS	  1		TARGET_LONG_DOUBLE_128
> > 
> >   Same here: any configurations with !TARGET_LONG_DOUBLE_128?
> 
> I wouldn't think so; glibc before version 2.4, circa 1998?

No idea about MIPS, but for ppc/ppc64/s390/s390x/sparc32 the selectable
size long double support is from 2006.

	Jakub