48e509c3fd
Per https://software.intel.com/en-us/blogs/2012/11/17/the-difference-between-rdrand-and-rdseed , RDRAND is a PRNG seeded from the same source as RDSEED. The source is more suitable as PRNG seed material, so prefer it when the RDSEED intrinsic is available (indicated in CPU feature bits). Reviewed by: delphij, jhb, imp (earlier version) Approved by: secteam(delphij) Security: yes Sponsored by: Dell EMC Isilon Differential Revision: https://reviews.freebsd.org/D20192