cselim: Handle clobbers too [PR122178]

cselim: Handle clobbers too [PR122178]

With the addition of cselim-limited in phiopt, factoring
out clobbers can be added easily. Now sink handles clobbers as
a store too. So this just moves that earlier.

This adds support there with a testcase to show it happens.

Bootstrapped and tested on x86_64-linux-gnu.

	PR tree-optimization/122178

gcc/ChangeLog:

	* tree-ssa-phiopt.cc (cond_if_else_store_replacement_1): Handle
	clobber statements.

gcc/testsuite/ChangeLog:

	* g++.dg/tree-ssa/cselim-1.C: New test.

Signed-off-by: Andrew Pinski <andrew.pinski@oss.qualcomm.com>