from patch provided by aarnez in #991

from patch provided by aarnez in #991

from patch provided by aarnez in #991

as reported by aarnez in #1990

as suggested in #1990

* Tag arguments 0 and 1 as both input and output

* Tag arguments 0 and 1 as both input and output (see #1964)

* Tag operands 0 and 1 as both input and output

For #1964 (basically a continuation of coding problems first seen in #1292)

Fixed idamin,icamin choosing the first occurance index of equal minimals

casting ints is cheaper but it has a rounding, not memory casing effect, resulting in
invalid outcome

The dgemm_ncopy_8_skylakex.c code is not avx512 specific and gives
a nice performance boost for medium sized matrices

it's more efficient for certain tall/skinny matrices

sgemm_ncopy_4_skylakex.c uses SSE transpose operations where the
real perf win happens; this also works great for Haswell.

This gives double digit percentage gains on small and skinny matrices

with a few small changes it's possible to use the skylake sgemm code
also for haswell, this gives a modest gain (10% range) for smallish
matrixes but does wonders for very skinny matrixes

OpenBLAS has a fancy algorithm for copying the input data while laying
it out in a more CPU friendly memory layout.

This is great for large matrixes; the cost of the copy is easily
ammortized by the gains from the better memory layout.

But for small matrixes (on CPUs that can do efficient unaligned loads) this
copy can be a net loss.

This patch adds (for SKYLAKEX initially) a "sgemm direct" mode, that bypasses
the whole copy machinary for ALPHA=1/BETA=0/... standard arguments,
for small matrixes only.

What is small? For the non-threaded case this has been measured to be
in the M*N*K = 28 * 512 * 512 range, while in the threaded case it's
less, around M*N*K = 1 * 512 * 512

Fix for DYNAMIC_ARCH builds made on a AVX512-capable host