Separate implementations of AMAX and IAMAX on arm

Fix detection of Skylake processors when using GCC

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.

for #2151

As noted in #1912 and comment on #1942, the combined implementation happens to "do the right thing" on hardfp, but cannot return both value and index on softfp where they would have to share the return register

Revert "Add softfp support in min/max kernels"

Add softfp support in min/max kernels

Build and run utests independently of fortran

fix for #1912

Do not try ancient PGI hacks with recent versions of that compiler

should fix #2139

Add option to allow combining USE_THREAD=0 with thread locking support

TST: add SkylakeX AVX512 CI test

for calling from concurrent threads

* adapt the C-level reproducer code for some
recent SkylakeX AVX512 kernel issues, provided
by Isuru Fernando and modified by Martin Kroeker,
for usage in the utest suite

* add an Intel SDE SkylakeX emulation utest run to
the Azure CI matrix; a custom Docker build was required
because Ubuntu image provided by Azure does not support
AVX512VL instructions

Drone CI for arm64 native builds

Move ARMv8/gcc CI job from Travis to Azure

Add NO_AFFINITY to available CMAKE options on Linux, and set it to ON