* Update to 20.1.8

* fix PATH to avoid the obsolete LLVM19 that appeared in the preinstalled msvc folder hierarchy

Signed-off-by: Han Gao <rabenda.cn@gmail.com>

* Add NeoverseN2 build

Uses Mermaid to render it as a diagram in the html docs.

The CLANG32 environment is in the process of being removed from MSYS2
currently:
https://www.msys2.org/news/#2024-09-23-starting-to-drop-the-clang32-environment

Remove it from the build matrix ahead of its complete removal from MSYS2.

Use microarchitecture name instead of meaningless strings to name the core,
the legacy core is still retained.
1. Rename LOONGSONGENERIC to LA64_GENERIC
2. Rename LOONGSON3R5 to LA464
3. Rename LOONGSON2K1000 to LA264

Implement DYNAMIC_ARCH support for riscv64.  Three cpu types are
supported, riscv64_generic, riscv64_zvl256b, riscv64_zvl128b.
The two non-generic kernels require CPU support for RVV 1.0 to
function correctly.  Detecting that a riscv64 device supports
RVV 1.0 is a little complicated as there are some boards on the
market that advertise support for V via hwcap but only support
RVV 0.7.1, which is not binary compatible with RVV 1.0.  The
approach taken is to first try hwprobe.  If hwprobe is not
available, we fall back to hwcap + an additional check to distinguish
between RVV 1.0 and RVV 0.7.1.

Tested on a VM with VLEN=256, a CanMV K230 with VLEN=128 (with only
the big core enabled), a Lichee Pi with RVV 0.7.1 and a VF2 with no
vector.

A compiler with RVV 1.0 support must be used to build OpenBLAS for
riscv64 when DYNAMIC_ARCH=1.

Signed-off-by: Mark Ryan <markdryan@rivosinc.com>

- Updates to latest versions for all actions
- Pin actions not maintained by GitHub under `github.com/action` to exact
  commit hashes. This is good practice for security, since tags can be
  moved and then arbitray new code may execute. Since updating commit
  hashes is slightly more hassle, the trade-off made here is to trust
  GitHub, but not third-party actions.

This should also solve the warnings about Node.js 16 actions being
deprecated that is currently visible on the log page when docs.yml
is executed.

Improve the stability and speed of testing

Compile the community version of QEMU to support LSX/LASX extension instructions

CI: Add clang test for loongarch64

Signed-off-by: Han Gao/Revy/Rabenda <rabenda.cn@gmail.com>