analyzer: Handle strdup builtins

analyzer: Handle strdup builtins

Consolidate allocator builtin handling and add support for
__builtin_strdup and __builtin_strndup.

gcc/analyzer/ChangeLog:

	* analyzer.cc (is_named_call_p, is_std_named_call_p): Make
	first argument a const_tree.
	* analyzer.h (is_named_call_p, -s_std_named_call_p): Likewise.
	* sm-malloc.cc (known_allocator_p): New function.
	(malloc_state_machine::on_stmt): Use it.

gcc/testsuite/ChangeLog:

	* gcc.dg/analyzer/strdup-1.c (test_4, test_5, test_6): New
	tests.