1. Remove the FADD insn from the GEMV Transpose code.
  2. Remove the FADD insn from GEMM and ZGEMM code.
  3. Reorder the compution of the Imaginary part in ZGEMM code.

This patch fixes following lapack failures with clang compiler on POWER.
zed.out: ZVX:   18 out of  5190 tests failed to pass the threshold
zgd.out: ZGV drivers:     25 out of   1092 tests failed to pass the threshold
zgd.out: ZGV drivers:      6 out of   1092 tests failed to pass the threshold

Fix regression SAXPY when compiler with OpenXL compiler.

SAXPY built with OpenXL regresses when compared to SAXPY
built with gcc. OpenXL compiler doesn't know that the
SAXPY inner kernel assembly is a 64 element loop and
to it the remainder loop is the main loop. It vectorizes
and interleaves the remainder to be a 48 elements per
iteration loop. With a max of 63 iterations, a 48 element
loop is mostly not going to get executed, so the 1 element
scalar loop that is the remainder after that is probably
mostly what gets executed.

This can be fixed by adding a pragma, loop interleave_count(2)
which will result in 8 element loop.

Signed-off-by: Amrita H S <amritahs@linux.vnet.ibm.com>

This reverts commit accea1555159d0928a6aa2db740c042c7e8f0dd3, reversing
changes made to b925353006.

Cgemm zgemm c code

Fixes: https://github.com/OpenMathLib/OpenBLAS/issues/4366

POWER10 optimizations are disabled when using default AIX assembler.
As we have fixed many issues recently, enabling optimization path
for default assembler.

As cgemm and zgemm kernels are not optimized for big endian falling
back to POWER8 versions.  Tested on AIX using gcc and Open XL C.

Modernize obsolete inline order

__builtin_vsx_assemble_pair was only in GCC 10-11.2 and was replaced by
__builtin_vsx_build_pair thereafter.