[WIP] Use arm neon instructions to optimize gemm beta operation

driver: more reasonable thread wait timeout on Windows.

It used to be 5ms, which might not be long enough in some cases for the
thread to exit well, but then when set to 5000 (5s), it would slow down
any program depending on OpenBlas.

Let's just set it to 50ms, which is at least 10 times longer than
originally, but still reasonable in case of failed thread termination.

Changes to build on AIX in POWER8 mode

Support two-digit version numbers in gcc version check

fixes #2336 (non-recognition of gcc 10) with patch provided by JeffreyALaw.

* Update DYNAMIC_ARCH list of ARM64 targets for gmake
* Update arm64 cpu list for runtime detection
* Update DYNAMIC_ARCH list of ARM64 targets for cmake and add POWERPC targets

Remove misplaced file

was originally in #2228 but that PR had misplaced the file in the toplevel directory

Rebase

Workaround an ICE in clang 9.0.0

This bug is not there in 8.x nor in the 9.0 daily snapshot.

Fix precompiled kernels on POWER9 and make their use conditional on (old) gcc version

Fix SEGV in cdot_power9