compiler: add containing Bfunction to some backend interfaces.

compiler: add containing Bfunction to some backend interfaces.

    Change the interfaces for backend methods that create statements to
    always pass in the enclosing Bfunction for the statement.  Having the
    function available simplifies things if a temporary variable has to be
    created during the construction of a statement.

    This also includes a change to the Mark_lvalue_varexprs helper
    class to handle indirections on the left hand side of assignments
    (e.g. "*x.y = ...").

    Reviewed-on: https://go-review.googlesource.com/34471

	* go-gcc.cc (Gcc_backend::expression_statement): Add Bfunction*
	parameter.
	(Gcc_backend::init_statement): Likewise.
	(Gcc_backend::assignment_statement): Likewise.
	(Gcc_backend::if_statement): Likewise.

From-SVN: r243766