compiler: Don't initialize zero sized variables.

compiler: Don't initialize zero sized variables.

	* go-gcc.cc (Gcc_backend::init_statement): Don't initialize a
	zero-sized variable.
	(go_non_zero_struct): New global variable.
	(Gcc_backend::non_zero_size_type): New function.
	(Gcc_backend::global_variable): Don't build an assignment for a
	zero-sized value.
	* go-c.h (go_non_zero_struct): Declare.
	* config-lang.in (gtfiles): Add go-c.h.

From-SVN: r185115