PHIOPT: Improve readability of tree_ssa_phiopt_worker

PHIOPT: Improve readability of tree_ssa_phiopt_worker

This small patch just changes around the code slightly to
make it easier to understand that the cases were handling diamond
shaped BB for both do_store_elim/do_hoist_loads.
There is no effect on code output at all since all of the checks
are the same still.

OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.

gcc/ChangeLog:

	* tree-ssa-phiopt.cc (tree_ssa_phiopt_worker):
	Change the code around slightly to move diamond
	handling for do_store_elim/do_hoist_loads out of
	the big if/else.