tree-optimization/116406 - ICE with int<->float punning prevention

The following does away with the idea to use non-symmetrical
testing of mode_can_transfer_bits in hash-table equality testing.
It isn't feasible to always control query order to maintain
consistency.

	PR tree-optimization/116406
	* tree-ssa-sccvn.cc (vn_reference_eq): Never equate
	float and int when the float mode cannot transfer bits.
	Do not try to anticipate which is the mode we actually load
	from.

	* gcc.dg/tree-ssa/pr116406.c: New testcase.
	* gcc.dg/tree-ssa/ssa-pre-30.c: On x86 dd -msse -mfpmath=sse.