Xeon Phi CPUs Support removed in GCC 15

[Prince213]

According to https://gcc.gnu.org/gcc-15/changes.html#x86:

Support for Xeon Phi CPUs (a.k.a. Knight Landing and Knight Mill) were removed in GCC 15. GCC will no longer accept -march=knl, -march=knm, -mavx5124fmaps, -mavx5124vnniw, -mavx512er, -mavx512pf, -mprefetchwt1, -mtune=knl, and -mtune=knm compiler switches.

This has already begun to affect downstream distros such as NixOS (NixOS/nixpkgs#475834), where we have to use genereic instead.

Are there any migration plans to newer CPU architectures?

[rgommers]

This is resolved upstream in BLIS: flame/blis#846. The three PRs linked from that issue could be synced to this repo, or perhaps easier to update the flame-blis git submodule to a recent commit. One of those three PRs is similar to what was done in gh-129.