Add trivially optimized DSDOT for POWER8

Add optimized dsdot to all other x86_64 kernels that use sdot.c

Eliminate warnings

Update LAPACK to 3.8.0

[appveyor] use cmake from conda forge

Handle shmem init failures in cpu affinity setup code

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

Eliminate mode variable where not needed in syrk interface

Change CBLAS complex functions to take void pointers

last parameter of cblas_(c,z)dotc_sub and cblas_(c,z)dotu_sub should be void* as well

Clean up spurious unused variables in the kernels

l2 cache size is not universally needed to assign default unrolling limits, but neither putting its declaration inside an ifdef nor cloning it into all ifdef sections that need it really makes sense here.

[appveyor] use flang from conda-forge

Break out of potentially infinite rescaling loop after 1000 iterations

Inf values in the input vector will survive rescaling, causing an infinite loop. The value of 1000 is arbitrarily chosen as a large but finite value with the intention to never interfere with regular calculations.

Try to handle shmget or shmat failing

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

This flang will be updated in the future. We leave cmake because it's
not yet released with fortran support

Output an error message when shmat() fails

Observed in #1351 with SELinux as the likely culprit. Without the message, the user saw a segfault with no apparent reason

WIP: Support for Flang on Windows