extend.texi (Function Attributes): Move @cindex after @item for 'artifical' and 'flatten'.

	* doc/extend.texi (Function Attributes): Move @cindex after @item
	for 'artifical' and 'flatten'. Fix grammar for 'externally_visible'
	and put in alphabetical order. Fix 'target' name and put in order.
	* doc/invoke.texi (-Wstrict-null-sentinel, -fipa-matrix-reorg): Fix
	typos.

From-SVN: r143051