Fix pessimization in EH cleanup pass

Fix pessimization in EH cleanup pass

This restores the post-order traversal done by cleanup_all_empty_eh in
order to eliminate empty landing pads and also contains a small tweak
to the line debug info to avoid a problematic inheritance for coverage
measurement.

gcc/ChangeLog:
	* tree-eh.c (lower_try_finally_dup_block): Backward propagate slocs
	to stack restore builtin calls.
	(cleanup_all_empty_eh): Do again a post-order traversal of the EH
	region tree.

gcc/testsuite/ChangeLog:
	* gnat.dg/concat4.adb: New test.