dce: Don't dead-code delete separately wrapped restores

dce: Don't dead-code delete separately wrapped restores

If there is a separately wrapped register restore on some path that
is dead (say, control goes into an endless loop after it), then we
cannot delete that restore because that would confuse the DWARF CFI
(if there is another path joining).
This happens with gcc.dg/torture/pr53168.c, for example.

	* dce.c (delete_unmarked_insns): Don't delete instructions with
	a REG_CFA_RESTORE note.

From-SVN: r241060