[20.10 FEAT] Algebra lib optimizations - OpenBlas (0.3.10) + enable DYNAMIC_ARCH=1

The OpenBlas library is the backend for many machine learning algorithms using the Numpy Python framework. The library has been enhanced to support z13 and partially z14 via BountySource. Measurements still show performance gaps compared to the maximum theoretical performance.

Addl. request:

Please enable "DYNAMIC_ARCH=1" for s390x to enable choosing the best performing
implementation at run-time (i.e., s390x should be added to
ENABLE_DYNAMIC_ARCHS). Current builds of openblas version 0.3.10+ds-3 for
groovy instead rely on generic floating-point instructions
(TARGET=ZARCH_GENERIC) and thus do not use the significant performance
potential of the SIMD instructions that were introduced with z13 and extended
with z14 (cf.
https://launchpadlibrarian.net/491360113/buildlog_ubuntu-groovy-s390x.openblas_0.3.10+ds-3_BUILDING.txt.gz)

While the mechanism for selecting the best implementation at run-time had some
deficits on s390x in the past, we have revised it in OpenBLAS 0.3.10 and
consider it the best choice for portable binaries.

Please note that there is a small bug in the s390-specific part of the Makefile
triggered with gcc-10 and DYNAMIC_ARCH=1, which has been fixed upstream in
June. The fix cleanly applies on top of 0.3.10 --
https://github.com/xianyi/OpenBLAS/pull/2669