Allow the front-end to create calls with a static chain

And, at the same time, allow indirect calls to have a static chain.
We'll always eliminate the static chain if we can prove it's unused.

        * calls.c (prepare_call_address): Allow decl or type for first arg.
        (expand_call): Pass type to prepare_call_address if no decl.
        * gimple-fold.c (gimple_fold_call): Eliminate the static chain if
        the function doesn't use it; fold it otherwise.
        * gimplify.c (gimplify_call_expr): Gimplify the static chain.
        * tree-cfg.c (verify_gimple_call): Allow a static chain on indirect
        function calls.

From-SVN: r217770