analyzer: fix setjmp-detection and support sigsetjmp

This patch removes the hack in is_setjmp_call_p of looking for
"setjmp" and "_setjmp", replacing it with some logic adapted from
special_function_p in calls.c, ignoring up to 2 leading underscores from
the fndecl's name when checking for a function by name.

It also requires that such functions are "extern" and at file scope
for them to be matched.

The patch also generalizes the setjmp/longjmp handling in the analyzer
to also work with sigsetjmp/siglongjmp.  Doing so requires generalizing
some hardcoded functions in diagnostics (which were hardcoded to avoid
user-facing messages referring to "_setjmp", which is an implementation
detail) - the patch adds a new function, get_user_facing_name for this,
for use on calls that matched is_named_call_p and
is_specical_named_call_p.

gcc/analyzer/ChangeLog:
	* analyzer.cc  (is_named_call_p): Check that fndecl is "extern"
	and at file scope.  Potentially disregard prefix _ or __ in
	fndecl's name.  Bail if the identifier is NULL.
	(is_setjmp_call_p): Expect a gcall rather than plain gimple.
	Remove special-case check for leading prefix, and also check for
	sigsetjmp.
	(is_longjmp_call_p): Also check for siglongjmp.
	(get_user_facing_name): New function.
	* analyzer.h (is_setjmp_call_p): Expect a gcall rather than plain
	gimple.
	(get_user_facing_name): New decl.
	* checker-path.cc (setjmp_event::get_desc): Use
	get_user_facing_name to avoid hardcoding the function name.
	(rewind_event::rewind_event): Add rewind_info param, using it to
	initialize new m_rewind_info field, and strengthen the assertion.
	(rewind_from_longjmp_event::get_desc): Use get_user_facing_name to
	avoid hardcoding the function name.
	(rewind_to_setjmp_event::get_desc): Likewise.
	* checker-path.h (setjmp_event::setjmp_event): Add setjmp_call
	param and use it to initialize...
	(setjmp_event::m_setjmp_call): New field.
	(rewind_event::rewind_event): Add rewind_info param.
	(rewind_event::m_rewind_info): New protected field.
	(rewind_from_longjmp_event::rewind_from_longjmp_event): Add
	rewind_info param.
	(class rewind_to_setjmp_event): Move rewind_info field to parent
	class.
	* diagnostic-manager.cc (diagnostic_manager::add_events_for_eedge):
	Update setjmp-handling for is_setjmp_call_p requiring a gcall;
	pass the call to the new setjmp_event.
	* engine.cc (exploded_node::on_stmt): Update for is_setjmp_call_p
	requiring a gcall.
	(stale_jmp_buf::emit): Use get_user_facing_name to avoid
	hardcoding the function names.
	(exploded_node::on_longjmp): Pass the longjmp_call when
	constructing rewind_info.
	(rewind_info_t::add_events_to_path): Pass the rewind_info_t to the
	rewind_from_longjmp_event's ctor.
	* exploded-graph.h (rewind_info_t::rewind_info_t): Add
	longjmp_call param.
	(rewind_info_t::get_longjmp_call): New.
	(rewind_info_t::m_longjmp_call): New.
	* region-model.cc (region_model::on_setjmp): Update comment to
	indicate this is also for sigsetjmp.
	* region-model.h (struct setjmp_record): Likewise.
	(class setjmp_svalue): Likewise.

gcc/testsuite/ChangeLog:
	* gcc.dg/analyzer/sigsetjmp-5.c: New test.
	* gcc.dg/analyzer/sigsetjmp-6.c: New test.