install.texi (Specific, [...]): Split from IRIX 5 section.

install.texi (Specific, [...]): Split from IRIX 5 section.

	* doc/install.texi (Specific, mips*-sgi-irix4): Split from IRIX 5
	section.
	(Specific, mips*-sgi-irix5): Note IDO download.
	Reworded MIPS C hints.
	Use GNU as instead of GAS.
	Markup fixes.
	Removed SGI Freeware reference, IRIX 6 only.
	(Specific, mips*-sgi-irix6): Removed ranlib caveats, obsolete.
	Note N64 library requirement/workaround.
	Update O32 hints.
	Complete list of structure passing bug victims.

From-SVN: r43694