Intel Xeon bug may segfault Sambamba

[pjotrp]

See #219

It is called BDF76 An Intel® Hyper-Threading Technology Enabled
Processor May Exhibit Internal Parity Errors or Unpredictable System
Behavior”. The symptoms described for this issue are very broad
(“unpredictable system behavior may occur”), but what we were
observing seemed to match the description of this issue better than
any other.

A microcode update is available. Also switching off hyperthreading
in the bios should fix it. There is no LLVM fix that I can find (Intel
says there is no possible fix available).

See also

https://www.intel.co.uk/content/www/uk/en/processors/xeon/xeon-e5-v4-spec-update.html
https://www.digitaltrends.com/computing/intel-hyperthreading-bug-kaby-skylake/

[pjotrp]

As this is an intel bug without a fix in llvm or gcc I'll close it. It is here for reference.