fix win center trap for elm to pass in h and v params

fix win center trap for elm to pass in h and v params

while this is technically an abi break, it should actually have no
real impact. it will have warnings - sure, but running existing code
will simply not see the extra parammeters on the stack and not use
them so it'll continue to work. if we removed paramms, we'd be in
pain. (same applies to params passed in registers).

this fixes T2031