c++: Fix detailed-mem-stat breakage

module.cc has a static initializer that ends up in a circular
dependency when detailed mem stats are enabled.  This removes the need
for that initializer to be dynamic, and we punt to the lazy
initializing we already had inside the object in question anyway.  At
the cost of an additional indirection.

	gcc/cp/
	* module.cc (loc_spans): Make spans a pointer, not inline.
	Adjust all accesses.