[PATCH] c++: implement C++17 hardware interference size

[Jonathan Wakely]

On Fri, 16 Jul 2021 at 03:51, Noah Goldstein wrote:
> On intel x86 systems with a private L2 cache the spatial prefetcher
> can cause destructive interference along 128 byte aligned boundaries.
> https://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-optimization-manual.pdf#page=60

Which is a good example of why these "constants" should never have
been standardized in the first place. Sigh.