Add statistics counting to PHI-OPT

Add statistics counting to PHI-OPT

This should have been done before I started to work on connecting
PHI-OPT to match-and-simplify to see quickly if we miss anything
but it is better late than never.
Anyways there was no statistics counting in PHI-OPT before so adding
it is the right thing to do.

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

gcc/ChangeLog:

	* tree-ssa-phiopt.c (replace_phi_edge_with_variable):
	Add counting of how many times it is done.
	(factor_out_conditional_conversion): Likewise.
	(match_simplify_replacement): Likewise.
	(value_replacement): Likewise.
	(spaceship_replacement): Likewise.
	(cond_store_replacement): Likewise.
	(cond_if_else_store_replacement_1): Likewise.
	(hoist_adjacent_loads): Likewise.