Add a suitable .def file for rustrt.dll on Windows

src/rt/rustrt.def

@@ -0,0 +1,70 @@
+LIBRARY RUSTRT
+EXPORTS
+	align_of
+	debug_box
+	debug_fn
+	debug_obj
+	debug_opaque
+	debug_ptrcast
+	debug_tag
+	debug_trap
+	debug_tydesc
+	do_gc
+	last_os_error
+	rand_free
+	rand_new
+	rand_next
+	refcount
+	rust_file_is_dir
+	rust_get_stdin
+	rust_get_stdout
+	rust_run_program
+	rust_start
+	size_of
+	str_alloc
+	str_buf
+	str_byte_len
+	str_from_buf
+	str_from_cstr
+	str_from_vec
+	task_sleep
+	unsupervise
+	upcall_clone_chan
+	upcall_del_chan
+	upcall_del_port
+	upcall_exit
+	upcall_fail
+	upcall_flush_chan
+	upcall_free
+	upcall_get_type_desc
+	upcall_grow_task
+	upcall_join
+	upcall_kill
+	upcall_log_int
+	upcall_log_str
+	upcall_malloc
+	upcall_mark
+	upcall_new_chan
+	upcall_new_port
+	upcall_new_str
+	upcall_new_task
+	upcall_new_thread
+	upcall_new_vec
+	upcall_recv
+	upcall_require_c_sym
+	upcall_require_rust_sym
+	upcall_send
+	upcall_sleep
+	upcall_start_task
+	upcall_start_thread
+	upcall_trace_str
+	upcall_trace_word
+	upcall_vec_grow
+	upcall_yield
+	vec_alloc
+	vec_alloc_mut
+	vec_buf
+	vec_len
+	vec_len_set
+	vec_print_debug_info
+