install.texi (Specific, [...]): Reflect working IRIX 5 port.

install.texi (Specific, [...]): Reflect working IRIX 5 port.

	* doc/install.texi (Specific, mips-sgi-irix5): Reflect working
	IRIX 5 port.
	Remove -save-temps workaround, handled automatically.
	Require GNU binutils 2.15 for debugging.
	Remove SGI make warnings since GNU make is now required.
	(Specific, mips-sgi-irix6): Some markup fixes.
	Describe MIPSpro C problems and workarounds.
	Mention working O32 ABI support.
	Recommend GNU as 2.15 for O32 with debugging.
	Remove description of fixed structure pass/return bug.

From-SVN: r80772