middle-end/111818 - failed DECL_NOT_GIMPLE_REG_P setting of volatile

middle-end/111818 - failed DECL_NOT_GIMPLE_REG_P setting of volatile

The following addresses a missed DECL_NOT_GIMPLE_REG_P setting of
a volatile declared parameter which causes inlining to substitute
a constant parameter into a context where its address is required.

The main issue is in update_address_taken which clears
DECL_NOT_GIMPLE_REG_P from the parameter but fails to rewrite it
because is_gimple_reg returns false for volatiles.  The following
changes maybe_optimize_var to make the 1:1 correspondence between
clearing DECL_NOT_GIMPLE_REG_P of a register typed decl and
actually rewriting it to SSA.

	PR middle-end/111818
	* tree-ssa.cc (maybe_optimize_var): When clearing
	DECL_NOT_GIMPLE_REG_P always rewrite into SSA.

	* gcc.dg/torture/pr111818.c: New testcase.

(cherry picked from commit ce55521bcd149fdc431f1d78e706b66d470210ae)