analyzer: fix ICE when longjmp isn't marked 'noreturn' (PR 93316)

Comments 11-16 within PR analyzer/93316 discuss an ICE in some setjmp
tests seen on AIX and powerpc-darwin9.

The issue turned out to be an implicit assumption that longjmp is
marked "noreturn".  There are two places in engine.cc where the code
attempted to locate the longjmp GIMPLE_CALL by finding the final stmt
within its supernode, in one place casting it via "as_a <gcall *>",
in the other using it as the location_t of the
"rewinding from longjmp..." event.

When longjmp isn't marked noreturn, its basic block and hence supernode
can have additional stmts after the longjmp; in the setjmp-3.c case
this was a GIMPLE_RETURN, leading to a ICE when casting this to a
GIMPLE_CALL.

This patch fixes the two places in question to use the
  rewind_info_t::get_longjmp_call
member function introduced by 342e14ff,
fixing the ICE (and ensuring the correct location_t is used for events).

gcc/analyzer/ChangeLog:
	PR analyzer/93316
	* engine.cc (rewind_info_t::update_model): Get the longjmp call
	stmt via get_longjmp_call () rather than assuming it is the last
	stmt in the longjmp's supernode.
	(rewind_info_t::add_events_to_path): Get the location_t for the
	rewind_from_longjmp_event via get_longjmp_call () rather than from
	the supernode's get_end_location ().

gcc/analyzer/ChangeLog

 2020-01-28  David Malcolm  <dmalcolm@redhat.com>
 
+	PR analyzer/93316
+	* engine.cc (rewind_info_t::update_model): Get the longjmp call
+	stmt via get_longjmp_call () rather than assuming it is the last
+	stmt in the longjmp's supernode.
+	(rewind_info_t::add_events_to_path): Get the location_t for the
+	rewind_from_longjmp_event via get_longjmp_call () rather than from
+	the supernode's get_end_location ().
+
+2020-01-28  David Malcolm  <dmalcolm@redhat.com>
+
 	* region-model.cc (poisoned_value_diagnostic::emit): Update for
 	renaming of warning_at overload to warning_meta.
 	* sm-file.cc (file_leak::emit): Likewise.

gcc/analyzer/engine.cc

@@ -1333,21 +1333,13 @@ void
 rewind_info_t::update_model (region_model *model,
 			     const exploded_edge &eedge)
 {
-  const exploded_node &src_enode = *eedge.m_src;
-  const program_point &src_point = src_enode.get_point ();
-
-  const gimple *last_stmt
-    = src_point.get_supernode ()->get_last_stmt ();
-  gcc_assert (last_stmt);
-  const gcall *longjmp_call = as_a <const gcall *> (last_stmt);
-
   const program_point &longjmp_point = eedge.m_src->get_point ();
   const program_point &setjmp_point = eedge.m_dest->get_point ();
 
   gcc_assert (longjmp_point.get_stack_depth ()
 	      >= setjmp_point.get_stack_depth ());
 
-  model->on_longjmp (longjmp_call,
+  model->on_longjmp (get_longjmp_call (),
 		     get_setjmp_call (),
 		     setjmp_point.get_stack_depth (), NULL);
 }
@@ -1368,7 +1360,7 @@ rewind_info_t::add_events_to_path (checker_path *emission_path,
 
   emission_path->add_event
     (new rewind_from_longjmp_event
-     (&eedge, src_point.get_supernode ()->get_end_location (),
+     (&eedge, get_longjmp_call ()->location,
       src_point.get_fndecl (),
       src_stack_depth, this));
   emission_path->add_event