Move clang/gfortran OpenMP dependency rewriting out of f_check

Enable autodetection of Zen 3/4 cpus as their AVX512 Intel counterparts

Put more build information into Makefile.conf_last

* rows = 0 or cols = 0 is now a legal input and
  takes quick return path
* Follow BLAS/LAPACK convention that the leading
  dimensions must be at least 1.

The `group` expression ensures that the cancel-in-progress
behavior is to only cancel if a new commit is pushed to the PR for
which the job is running, not other PRs.

This is a fairly standard snippet, used also in CI jobs for NumPy
and other projects.

This is a follow-up to gh-4271. At the moment, when a contributor
pushes the latest `develop` to their own branch to bring their own
fork in sync with `main`, or if they push another branch, this triggers
30 CI jobs to run. Most will complete silently and only burn CPU
time unnecessarily. If there's a failure, this may result in unexpected
failure notifications. And the AWS Graviton3 run won't complete at all
and time out, since the Cirun hook will only work when triggered from
the main repo.

Fix FCOMMON_OPT for power.  Error out for certain C and Fortran compiler combos on AIX

Only define __builtin_cpu_is and __builtin_cpu_supports if not present.

(Re)apply Makefile fix for supporting only a subset of precision types

Correct constant ALPHA in ?ORBDB6 (Reference-LAPACK PR 928)

Fix accumulation in LAPACK ?LASSQ (Reference-LAPACK PR 909)

Fix potential integer overflow in LAPACK C/ZBDSQR (Reference-LAPACK PR 927)

* Clean up ZROTG

Use SkylakeX ?ASUM microkernel for Cooperlake/Sapphirerapids as well

Fix outdated KERNEL files for SVE Cortex by aliasing to ARMV8SVE

Add dynamic dispatch to AIX and clang for Power

CirrusCI: Add FreeBSD clang/gfortran build with OpenMP

Increase the default GEMM buffer size on modern ARM server cpus

Clarify make/make install in the README and update the TARGET list there

POWER: AIX: Make use of power10 optimization

POWER10 optimizations are disabled when using default AIX assembler.
As we have fixed many issues recently, enabling optimization path
for default assembler.

Run nightly Homebrew cron job only on the main repo, not on forks