Spectre variants 3a and 4

Intel has, finally, disclosedtwo more Spectre variants, called 3a and 4. The first ("rogue systemregister read") allows system-configuration registers to be readspeculatively, while the second ("speculative store bypass") could enablespeculative reads to data after a store operation has been speculativelyignored. Some more information on variant 4 can be found in theProject Zero bug tracker. The fix is to install microcode updates,which are not yet available.