So we choose strncpy(_, _, 0): it requires an extra header,
	but it's standard and should be very efficient.

	GCC 7 has an unfortunate habit of optimizing out strncpy calls (see
	https://golang.org/issue/21196), so the arguments here need to be global
	variables with external linkage in order to ensure that the call traps all the
	way down into libc.
	*/
	strncpy(&x_cgo_yield_strncpy_dst, &x_cgo_yield_strncpy_src,