When using cgo, Go must not assume that it owns all details of the
process. In particular it needs to coordinate with C in the use of
threads and thread-local storage. The runtime package declares a few
variables:

	var (
		iscgo             bool
		_cgo_init         unsafe.Pointer
		_cgo_thread_start unsafe.Pointer
	)

Any package using cgo imports "runtime/cgo", which provides