Remove obsolete IRIX 6.5 support

[Joseph S. Myers]

On Mon, 12 Mar 2012, Rainer Orth wrote:

> 	* config/mips/mips-modes.def: Remove IRIX 6 reference.
> 	* config/mips/gnu-user64.h (MIPS_TFMODE_FORMAT): Remove.
> 	* config/mips/mips.c (mips_option_override) [MIPS_TFMODE_FORMAT]:
> 	Remove.

I think this means that mips_extended_format in real.[ch] - the MIPS 
variant of IBM long double - is also obsolete, and with it all the support 
in fp-bit.[ch] for that format (__LDBL_MANT_DIG__ == 106 conditional, 
HALFFRACBITS, HALFSHIFT and associated conditional code).

-- 
Joseph S. Myers
joseph@codesourcery.com