There are two instances when building the tests where OpenBLAS fails to
build with OpenMP and clang due to library paths getting reset as flags
are set rather than appended. This seems to only affect certain
clang/libomp installations, but if it's already grabbing the correct
library paths we might as well use them.

This patch enables bfloat16 kernels by default for POWER processors.
Tested on Linux POWER8, POWER9, POWER10 and AIX POWER10 systems.

* limit flang optimizations to -O2

* Prevent addition of a BOM to test input (which would distort the names of output files)

add misc fixes.

Change-Id: Iae7800a32f5af3903c330882cdf6f292d885f266

This patch fixes compilation errors due to recent renaming from SH to SB
with BUILD_BFLOAT16.

replaces calculation of machine precision with call to epsilon intrinsic and removes the requirement for previous output files to be removed before rerunning tests

This patch adds another check to test shgemm results.

This patch has Makefile changes to add test for shgemm which
compares sgemm and shgemm result.

This patch adds support for bfloat16 data type matrix multiplication kernel.
For architectures that don't support bfloat16, it is defined as unsigned short
(2 bytes).  Default unroll sizes can be changed as per architecture as done for
SGEMM and for now 8 and 4 are used for M and N.  Size of ncopy/tcopy can be
changed as per architecture requirement and for now, size 2 is used.

Added shgemm in kernel/power/KERNEL.POWER9 and tested in powerpc64le and
powerpc64.  For reference, added a small test compare_sgemm_shgemm.c to compare
sgemm and shgemm output.

This patch does not cover OpenBLAS test, benchmark and lapack tests for shgemm.
Complex type implementation can be discussed and added once this is approved.

Found via `codespell -q 3 -w -L ith,als,dum,nd,amin,nto,wis,ba -S ./relapack,./kernel,./lapack-netlib`