Introduced callback to Pthread, Win32 and OpenMP backend

* Add all-in-one version of utest_ext for AIX

Align Makefile build options for embedded (Cortex M)  systems with the CMAKE code

Change xlf compiler to xlf_r in README for AIX.

* Add preliminary implementation of WhereAmI()

Fix uninitialized variables in LAPACK tests for ?QP3RK (Reference-LAPACK PR 961)

mips64: Fixed MSA optimization bugs for zgemv and cgemv

* Exit early if INCX <= 0

CI: add openblas_utest_ext for c910v, mips64 and loongarch64

Fix uninitialized variables in the extensions utest

Add another object signature for classic flang

revert the C/Z NRM2 kernels for NEOVERSEN1 and VORTEX to the base NEON kernel as well

remove extraneous suffix from shared object SONAME

Set GEMM_PREFERED_SIZE parameter for Neoverse V1

Remove -openmp flag from XLF (since it doesn't support it).

loongarch: Optimizing the performance of the GEMM on servers

Get the l2 cache size via environment variable on confidential VM

Don't pass `-exhaustive-register-search` directly to clang compiler

Retain the bf16 in fallback versions of the NeoverseN2 -march flag

Do not run the CBLAS_?GEMM3M tests when cross-compiling with gmake

Make the new ZSCAL utest not require CBLAS

`-exhaustive-register-search` is an LLVM code generation flag that shouldn't be passed directly to clang compiler.

The CPUID(leaf:2 or leaf:0x80000006) is not supported on some confidential
VMs. As a result the get_l2_size() returns the default 512M which brings
performance issues.

Introduce the environment variable OPENBLAS_L2_SIZE provided by the user
to get the l2 cache size.

Suggested-by: "Keshavamurthy, Anil S" <anil.s.keshavamurthy@intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>

Fold wiki contents into formal documentation, build-able with `mkdocs`

merge back from release branch to copy tag