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
initializations for these variables. It sets iscgo to true, _cgo_init
to a gcc-compiled function that can be called early during program