analyzer: fixes to -fdump-analyzer-state-purge for phi nodes

analyzer: fixes to -fdump-analyzer-state-purge for phi nodes

gcc/analyzer/ChangeLog:
	* state-purge.cc (state_purge_annotator::add_node_annotations):
	Rather than erroneously always using the NULL in-edge, determine
	each relevant in-edge, and print the appropriate data for each
	in-edge.  Use print_needed to print the data as comma-separated
	lists of SSA names.
	(print_vec_of_names): Add "within_table" param and use it.
	(state_purge_annotator::add_stmt_annotations): Factor out
	collation and printing code into...
	(state_purge_annotator::print_needed): ...this new function.
	* state-purge.h (state_purge_annotator::print_needed): New decl.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>