warn-access: wrong -Wdangling-pointer with labels [PR106080]

warn-access: wrong -Wdangling-pointer with labels [PR106080]

-Wdangling-pointer warns when the address of a label escapes.  This
causes grief in OCaml (<https://github.com/ocaml/ocaml/issues/11358>) as
well as in the kernel:
<https://bugzilla.kernel.org/show_bug.cgi?id=215851> because it uses

  #define _THIS_IP_  ({ __label__ __here; __here: (unsigned long)&&__here; })

to get the PC.  -Wdangling-pointer is documented to warn about pointers
to objects.  However, it uses is_auto_decl which checks DECL_P, but DECL_P
is also true for a label/enumerator/function declaration, none of which is
an object.  Rather, it should use auto_var_p which correctly checks VAR_P
and PARM_DECL.

	PR middle-end/106080

gcc/ChangeLog:

	* gimple-ssa-warn-access.cc (is_auto_decl): Remove.  Use auto_var_p
	instead.

gcc/testsuite/ChangeLog:

	* c-c++-common/Wdangling-pointer-10.c: New test.
	* c-c++-common/Wdangling-pointer-9.c: New test.