Fix a call to EmitVFPTruncate() that was passing the same register
in to the result_ref and scratch parameters causing the code to
always determine the input was not an Int32, regardless of whether
it was or not.

This caused some BinaryOpStub executions to trigger a transition
on each execution severely slowing the execution and potentially
preventing optimization of enclosing functions.
Merge remote branch 'origin/master'