[third_party][jitterentropy] jitterentropy library

Source: https://github.com/smuellerDD/jitterentropy-library
Commit: 3804c8408e0152173ce9690c4618cc45541da2e8
License: Dual-licensed GPLv2/BSD-3-Clause
Version: 2.1.0

Note: code from the upstream project that was released under non-BSD
licenses was removed. See README.fuchsia.

Change-Id: I6029d2e252bdaca2477b56a82cf73fff84e300a4