random: fix crash on some 64bit platforms
random: fix crash on some 64bit platforms

rbx needs to be stashed in a 64bit register on 64bit platforms. With this crash
in particular, it was holding a stack canary which was not properly restored
after the cpuid.

Split out the x86+PIC case so that x86_64 doesn't have to worry about it.

Mrs-X/PIVX,PIVX-Project/PIVX,Mrs-X/PIVX,Darknet-Crypto/Darknet,Darknet-Crypto/Darknet,Darknet-Crypto/Darknet,Mrs-X/Darknet,Mrs-X/PIVX,PIVX-Project/PIVX,PIVX-Project/PIVX,Darknet-Crypto/Darknet,Mrs-X/PIVX,Mrs-X/Darknet,Mrs-X/Darknet,PIVX-Project/PIVX,PIVX-Project/PIVX,Darknet-Crypto/Darknet,Mrs-X/Darknet,Mrs-X/Darknet,PIVX-Project/PIVX,Mrs-X/PIVX,PIVX-Project/PIVX,PIVX-Project/PIVX,Mrs-X/Darknet,Darknet-Crypto/Darknet,PIVX-Project/PIVX,Mrs-X/PIVX