builtin-types.def (BT_FN_VOID_CONST_PTR_VAR): Replace BT_FN_VOID_PTR_VAR.

        * builtin-types.def (BT_FN_VOID_CONST_PTR_VAR): Replace
        BT_FN_VOID_PTR_VAR.
        * builtins.def (BUILT_IN_PREFETCH): Change first argument to be const.
        * doc/extend.texi (__builtin_prefetch): Update documentation:
        first argument is now const void ptr.

        * gcc.c-torture/execute/builtin-prefetch-1.c: Changed first
        argument to __builtin_prefetch to be const ptr.

From-SVN: r49296