This patch adds the basic infrastructure for adding the SkylakeX (Intel Skylake server)
target. The SkylakeX target will use the AVX512 (AVX512VL level) instruction set,
which brings 2 basic things:
1) 512 bit wide SIMD (2x width of AVX2)
2) 32 SIMD registers (2x the number on AVX2)

This initial patch only contains a trivial transofrmation of the Haswell SGEMM kernel
to AVX512VL; more will follow later but this patch aims to get the infrastructure
in place for this "later".

Full performance tuning has not been done yet; with more registers and wider SIMD
it's in theory possible to retune the kernels but even without that there's an
interesting enough performance increase (30-40% range) with just this change.

This reverts commit e5752ff9b3.

The variables i and n are used in the `#if !__GLIBC_PREREQ(2, 7)`
branch.

Closes gh-1586.

fixes #1503

Add threading and OpenMP information to output

For #1416 and #1529, more information about the options OpenBLAS was built with is needed. Additionally we may want to add this data to the openblas.pc file (but not all projects use pkgconfig, and as far as I am aware the cmake module for accessing it does not make such "private" declarations available)

Change-Id: Id3fa4e8d9eedd4ef7230df69b611e7f397301a42

Fix race condition in blas_server_omp.c

Use _Atomic instead of volatile for thread safety where C11 is supported

Change-Id: Ic896276cd073d6b41930c7c5a29d66348cd1725d

Catch invalid cpu count returned by CPU_COUNT_S

mips32 was seen to return zero here, driving nthreads to zero with subsequent fpe in blas_quickdivide

Allow building on OpenBSD

With this change, OpenBLAS builds and all tests pass on OpenBSD 6.2
using Clang. Tested on x86-64 only, with and without DYNAMIC_ARCH=1.

Old gcc and clang do not handle constructor arguments, finally fix #875 as discussed there, using the fedora patch

Suggested by dodomorandi in #660

to migitate performance problems caused by #1052 and #1299 as seen in #1461

Even if we're directly using the win32 threading driver and not pthreads,
pthread_atfork still works fine to register a pre-fork handler, and is
necessary to restore the threading server to a pre-initialized state.

Initialize unitialized values for repeated calls

Address warnings #1357

Address few more warnings

* Calculation of chunk range limits was ignoring num_cpu

bug introduced by me in #1262 - should fix #1388

* Calculation of range limits was ignoring num_cpu

bug introduced by me in #1262

* Calculation of chunk range limits was ignoring num_cpu

bug introduced by me in #1262

* Calculation of chunk range limits was ignoring num_cpu

bug introduced by me in #1262

* Calculation of chunk range limits was ignoring num_cpu

bug introduced by me in #1262

* Calculation of chunk range limits was ignoring num_cpu

bug introduced by me in #1262

* dead increments in driver/level2

* dead increments in kernel/generic

* part dead increments in kernel/x86_64

Work around errors in multithreaded dtrmv

Some Linux distributions (notably SuSE) have raised CPU_SETSIZE to 4096, apparently disregarding API limitations.
From #1348, the highest value to survive array initialization (on a desktop system) is 3232, and 1024 - which is the 
more usual CPU_SETSIZE limit, was demonstrated to work fine on an actual bignuma system.

as a (hopefully temporary) workaround for #1332

Failures to obtain or attach shared memory segments would lead to an exit without explanation of the exact cause.
This change introduces a more verbose error message and tries to make the code continue without setting cpu affinity.
Fixes #1351

also replaces one verbatim sched_yield with the YIELDING macro for consistency as suggested in #1351

2D thread distribution for multi-threaded GEMMs

CMake improvements