tree-optimization/107153 - autopar SSA update issue

tree-optimization/107153 - autopar SSA update issue

autopar performs insertion of stores, eventually requiring a
virtual loop PHI and assorted LC PHI adjustments which we intend
to do once after the pass finishes.  But we also perform intermediate
update_ssa after loop duplication which can lose this fact.  The
following forces renaming of the virtual operand before the final
SSA update to fix that.  It also removes the explicit update_ssa
call from the gimple_duplicate_sese_tail utility as has been done
for all other such utilities and instead performs the SSA update
from autopar.

	PR tree-optimization/107153
	* tree-cfg.cc (gimple_duplicate_sese_tail): Do not update
	SSA form here.
	* tree-parloops.cc (gen_parallel_loop): Update SSA form
	after to-exit-first transform, no PHI insertion is necessary.
	(pass_parallelize_loops::execute): Force re-write of the
	virtual operand SSA web.

	* gcc.dg/autopar/pr107153.c: New testcase.