Fix a nasty order of evaluation bug that Gabor Greif ran into. Here's an

explanation from IRC:

	|sabre|	I think it's an order of evaluation thing
	|sabre|	for me, the RHS of the assignment is evaluated first
	|sabre|	getTypeDescription checks to see if ConcreteTypeDescription[Ty] contains anything
	|sabre|	since it doesn't, it computes and returns the value
	|sabre|	this gets put into the map.
	|sabre|	For you, the LHS is evaluated first.
	|sabre|	Map[Ty] (aka ConcreteTypeDescriptions[Ty]) inserts an empty string into the map, returning a reference
	|sabre|	getTypeDesc then sees the empty string in the map
	|sabre|	and returns it
	|sabre|	bork :)

llvm-svn: 20394