compiler: Use backend interface for defining global declarations.

	* go-gcc.cc: Include "cgraph.h" and "gimplify.h".
	(Gcc_backend::return_statement): Push and pop function.
	(Gcc_backend::label): Likewise.
	(Gcc_backend::function_defer_statement): Likewise.
	(Gcc_backend::switch_statement): Add function parameter.
	(Gcc_backend::block): Don't permit function to be NULL.
	(Gcc_backend::temporary_variable): Change go_assert to
	gcc_assert.
	(Gcc_backend::gc_root_variable): New function.
	(Gcc_backend::write_global_definitions): New function.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@209819 138bc75d-0d04-0410-961f-82ee72b054a4