analyzer: reimplement kf_strlen [PR105899]

analyzer: reimplement kf_strlen [PR105899]

Reimplement kf_strlen in terms of the new string scanning
implementation, sharing strlen's implementation with
__analyzer_get_strlen.

gcc/analyzer/ChangeLog:
	PR analyzer/105899
	* kf-analyzer.cc (class kf_analyzer_get_strlen): Move to kf.cc.
	(register_known_analyzer_functions): Use make_kf_strlen.
	* kf.cc (class kf_strlen::impl_call_pre): Replace with
	implementation of kf_analyzer_get_strlen from kf-analyzer.cc.
	Handle "UNKNOWN" return from check_for_null_terminated_string_arg
	by falling back to a conjured svalue.
	(make_kf_strlen): New.
	(register_known_functions): Use make_kf_strlen.
	* known-function-manager.h (make_kf_strlen): New decl.

gcc/testsuite/ChangeLog:
	PR analyzer/105899
	* gcc.dg/analyzer/null-terminated-strings-1.c: Update expected
	results on symbolic values.
	* gcc.dg/analyzer/strlen-1.c: New test.

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