New warning: -Wanalyzer-jump-through-null [PR105947]

This patch adds a new warning to -fanalyzer for jumps through NULL
function pointers.

gcc/analyzer/ChangeLog:
	PR analyzer/105947
	* analyzer.opt (Wanalyzer-jump-through-null): New option.
	* engine.cc (class jump_through_null): New.
	(exploded_graph::process_node): Complain about jumps through NULL
	function pointers.

gcc/ChangeLog:
	PR analyzer/105947
	* doc/invoke.texi: Add -Wanalyzer-jump-through-null.

gcc/testsuite/ChangeLog:
	PR analyzer/105947
	* gcc.dg/analyzer/function-ptr-5.c: New test.

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