for #2154

21eda8b5 introduced a check in getarch.c to test if the compiler is capable of
AVX512. This check currently fails, since the used __AVX2__ macro is only
defined if getarch itself was compiled with AVX2/AVX512 support. Make sure this
is the case by building getarch with -march=native on x86_64. It is only
supposed to run on the build host anyway.

Found via `codespell -q 3 -w -L ith,als,dum,nd,amin,nto,wis,ba -S ./relapack,./kernel,./lapack-netlib`

Add (C)BLAS extension ?sum

Add -lm and disable EXPRECISION support on *BSD

fixes #2075

for #2056, using same approach as #2058

e.g. cmake -DDYNAMIC_ARCH=1 -DDYNAMIC_LIST="NEHALEM;HASWELL;ZEN" ..
original issue was #1639

Fixed core naming for DYNAMIC_ARCH. Corrected GEMM_DEFAULT entries and added SYMV_P. Replaced outdated VULCAN define for ThunderX2T99 with ARMV8 to get basic definitions back. For issue #1908

Add -mavx2 to TARGET=HASWELL builds

and create config target directory for cross-compiles.

cf #1908

* Handle Android environments that identify as Linux

termux terminal emulator does this, causing build failures through missed defines in common.h

Use KERNEL_DEFINITIONS rather than COMMON_OPTS to pass -march=skylake…

Add -march=skylake-avx512 to CFLAGS when the target is Skylake

Should fix 1806 and #1801

Add -march=skylake-avx512 when required

fixes #1797

Check for Immintrin.h presence in the AVX512 compatibility test as well

Do not treat WIndows UWB builds as cross-compiling

Move some x86_64 DYNAMIC_ARCH targets to new DYNAMIC_OLDER option

Initial support for SkylakeX / AVX512

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.

Add build-time configuration options to pkgconfig file

Change-Id: Ic896276cd073d6b41930c7c5a29d66348cd1725d

Without specifying thread count, NUM_THREADS would not be defined and CMake would fail.
This is because core count cannot be determined when cross-compiling.