analyzer: fix ICE with incorrect lookup of cgraph node [PR105074]

gcc/analyzer/ChangeLog:
	PR analyzer/105074
	* region.cc (ipa_ref_requires_tracking): Drop "context_fndecl",
	instead using the ref->referring to get the cgraph node of the
	caller.
	(symnode_requires_tracking_p): Likewise.

gcc/testsuite/ChangeLog:
	PR analyzer/105074
	* gcc.dg/analyzer/pr105074.c: New test.
	* gcc.dg/analyzer/untracked-1.c (extern_fn_char_ptr): New decl.
	(test_13): New.

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