tree-optimization/109434 - bogus DSE of throwing call LHS

tree-optimization/109434 - bogus DSE of throwing call LHS

The byte tracking of call LHS didn't properly handle possibly
throwing calls correctly which cases bogus DSE and in turn, for the
testcase a bogus uninit diagnostic and (unreliable) wrong-code.

	PR tree-optimization/109434
	* tree-ssa-dse.cc (initialize_ao_ref_for_dse): Properly
	handle possibly throwing calls when processing the LHS
	and may-defs are not OK.

	* g++.dg/opt/pr109434.C: New testcase.