Use backend interface for variables.

Use backend interface for variables.

	* go-gcc.cc: Include "go-c.h".
	(class Bvariable): Define.
	(Gcc_backend::init_statement): New function.
	(Gcc_backend::global_variable): New function.
	(Gcc_backend::global_variable_set_init): New function.
	(Gcc_backend::local_variable): New function.
	(Gcc_backend::parameter_variable): New function.
	(tree_to_type, var_to_tree): New functions.
	* Make-lang.in (go/go-gcc.o): Depend on $(GO_C_H).
	* (go/gogo-tree.o): Depend on go/gofrontend/backend.h.

From-SVN: r172693