rebase

Unify BUFFER_SIZE settings for x86_64 again to fix DYNAMIC_ARCH crashes

Patch for building on POWERPC with PGI compilers (was Patch for building on Summit)

Add detection of stdatomic.h for cmake

rebase

Have c_check probe availability of C11 atomics support and stdatomic.h

Update cross-compiling example in README to reflect change in Loongson gcc

for #2723

Handle lack of fortran compiler more gracefully in cmake

Add new linker option for POWER10

While building with DYNAMIC_ARCH on POWER9 with POWER10
aware toolchain, new LDFLAG is needed to avoid POWER10
instructions on PLT calls .

rebase

[WIP] fix compilation on AIX

Add flang build to Github Actions

Fix OpenMP builds defaulting to singlethreading with OMP_PLACES or OMP_PROC_BIND set

Add LAPACK-TESTING to the cmake build

Change minimum gcc version for POWER10

As the MMA patches for POWER10 are backported to gcc10.2, changing
the minimum gcc version needed to build OpenBLAS for POWER10.

Changing mcpu option as power10

As compiler enabled mcpu option as power10, changing it from future.

Always obey omp_get_max_threads() when build with USE_OPENMP