aarch64: Further fix for throwing insns in ldp/stp pass [PR113217]

As the PR shows, the fix in
r14-6916-g057dc349021660c40699fb5c98fd9cac8e168653 was not complete.
That fix was enough to stop us trying to move throwing accesses above
nondebug insns, but due to this code in try_fuse_pair:

  // Placement strategy: push loads down and pull stores up, this should
  // help register pressure by reducing live ranges.
  if (load_p)
    range.first = range.last;
  else
    range.last = range.first;

we would still try to move stores up above any debug insns that occurred
immediately after the previous nondebug insn.  This patch fixes that by
narrowing the move range in the case that the second access is throwing
to exactly the range of that insn.

Note that we still need the fix to latest_hazard_before mentioned above
so as to ensure we select a suitable base and reject pairs if it isn't
viable to form the pair at the end of the BB.

gcc/ChangeLog:

	PR target/113217
	* config/aarch64/aarch64-ldp-fusion.cc
	(ldp_bb_info::try_fuse_pair): If the second access can throw,
	narrow the move range to exactly that insn.

gcc/testsuite/ChangeLog:

	PR target/113217
	* g++.dg/pr113217.C: New test.