Update the riscv-collab llvm toolchain in CI to its latest nightly build

Update Mac CI jobs as cmake is preinstalled in the runner images now

There were a couple of issues with the detection code used to check
for RVV 1.0 on kernels that do not support hwprobe.

1. The vtype clobber was missing
2. The wrong form of vsetvli was being used. The vsetvli x0, x0 form
   is inappropriate for this use case as it can only be safely used
   in code where the value of vtype is known.  The use of vsetvli
   x0, x0 here can lead to a failure to detect RVV 1.0, if,
   for example, the vill bit happens to be set before
   detect_riscv64_rvv100 is called.

We fix both issues by adding the missing clobber and replacing the
first parameter to vsetvli with t0 (which we add to our clobbers).

Implementing SVE in `[SD]AXPY` Kernels for `A64FX` and `Graviton3E`

Optimize the gemv_t_vector.c  kernel  for  RISCV64_ZVL256B target

Increase L2 defaults for RISCV X280 / ZVL256B and ARM SVE targets in CMake cross-compilation

fix: broken cblas installation when using makefile based builds

Add and use vectorized packing in ZVL128B and ZVL256B for RISCV

Move the value assignment of vector x in gemv_n_sve.c to the outermos…

Optimize SBGEMM / BGEMM for NEOVERSEV1 further

Fix cblas.h missing from target directory if NO_CBLAS is defined but has
a value that indicates you do want cblas built and installed.

1.Verify correctness using BLAS-Tester
    2.Using the built-in benchmark to verify performance, the performance of float and doule type improved by about 60% and about 40% respectively.The test command is:
     export OMP_NUM_THREADS=1;numactl -C 10 -l ./sgemv.goto 3000 4000 100
     export OMP_NUM_THREADS=1;numactl -C 10 -l ./dgemv.goto 3000 4000 100

This changes the kernels to pack full SVE vectors and reduces the
overall complexity of the inner GEMM loop.

* Update to 20.1.8

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

Fix compilation of the NeoverseN2 SBGEMM kernel

Multi-thread Performance Improvement of GEMM on NeoverseV1 with DIVIDE_RATE=1

Adjust multithreading threshold in S/DGER and add an intermediate step

Work around gcc15.1 on POWER misoptimizing DGEMV at -O3

Fix bad vector zero initializer and other compiler warnings for RISC-V.

Fix building of bgemm tests on GEMM3M-capable (x86) targets

ARM64: Enable bfloat16 kernels by default

Introduce a (crude) threshold to multithreading in STRMV/DTRMV

Add NEOVERSEV2 target support

Include float-bfloat conversion functions in ONLY_CBLAS builds as well

Add optimized BGEMM for NEOVERSEN2 target