libphobos: Select the appropriate exception handler in getClassInfo

This is analogous to __gdc_personality, which ignores in-flight
exceptions that we haven't collided with yet.

libphobos/ChangeLog:

	* libdruntime/gcc/deh.d (ExceptionHeader.getClassInfo): Move to...
	(getClassInfo): ...here as free function.  Add lsda parameter.
	(scanLSDA): Pass lsda to actionTableLookup.
	(actionTableLookup): Add lsda parameter, pass to getClassInfo.
	(__gdc_personality): Remove currentCfa variable.