analyzer: support diagnostics that don't have a stmt

analyzer: support diagnostics that don't have a stmt

gcc/analyzer/ChangeLog:
	* analyzer.cc (get_stmt_location): Handle null stmt.
	* diagnostic-manager.cc (saved_diagnostic::saved_diagnostic): Copy
	m_loc from ploc.
	(saved_diagnostic::operator==): Compare m_loc.
	(saved_diagnostic::calc_best_epath): Only use m_stmt_finder if
	m_loc is unknown.
	(dedupe_key::dedupe_key): Initialize m_loc.
	(dedupe_key::operator==): Compare m_loc.
	(dedupe_key::get_location): Use m_loc if it's known.
	(dedupe_key::m_loc): New field.
	(diagnostic_manager::emit_saved_diagnostic): Only call
	get_emission_location if m_loc is unknown, preferring to use m_loc
	if it's available.
	* diagnostic-manager.h (saved_diagnostic::m_loc): New field.
	(pending_location::pending_location): Initialize m_loc.  Add
	overload taking a location_t rather than a stmt/stmt_finder.
	(pending_location::m_loc): New field.

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