We need this for clock_gettime_nsec_np().
The source is not canonical, but neither was the one we were using
before. To mitigate this, I've added a digest check on the SDK after
downloading it.
A 100% real canonical reproducible build process will probably
require Apple hardware anyway.
Closes#221
Previously I'd hoped to have it only apply to reproducible builds,
but the work of keeping it up-to-date and checking it for drift
seems to have been tripping us up. Let's try doing it the other way
for now, and we'll see how that goes.
Linux hash : c024778da162cda77869c46d162729d012a7758bee973bc83fa78c964d080903
Windows hash : e97e171740b889b7e3722b79c3763177174baac7fa34a5c3615c999298e1bc48
Nick Mathewson
Dimitris Apostolou
Trinity Pointard