[WIP]Make NAN handling in the SCAL kernels depend on the dummy2 parameter

* avoid setting nthreads higher than available

Commit def4996 fixed issues with inf and nan values in zscal,
but used FLT_MAX, where DBL_MAX or isinf() is more appropriate,
as FLT_MAX is for single precision only.
Using FLT_MAX caused test case failures in the LAPACK tests.

isinf() is consistent with the later fix 969601a1

This fixes a (cross-)compilation/linker error for PRESCOTT
on Yocto.

Signed-off-by: Zoltán Böszörményi <zoltan.boszormenyi@xenial.com>

Fixed handling of NAN and INF arguments when
inc is greater than 1.

Check compiler support for AVX512BF16 and base COL/SPR kernel choice on that

for skylake kernels. This is the same method as used in [sd]asum.
_mm_set1_epi64x was commented out for zasum, but has the advantage
of avoiding possible undefined behaviour (using an uninitialized
variable), optimized out by NVHPC and icx. The new code works
fine with those compilers.

For GCC 12.3 the generated code is identical; no matter what method
you use, the compiler optimizes the code into a compile-time
constant, there is no performance benefit using mm_cmpeq_epi8
since the corresponding instruction (VPCMPEQB) isn't actually
generated!

* Temporarily disable the C/ZASUM microkernels for any version of NVHPC

This kernel is only used on Skylake+ if the kernel with AVX512
intrinsics can't be used, but used the variable x1 incorrectly
in the tail end of the loop, as it is still at the initial
value instead of where x points to.

This caused 55 "other error"s in the LAPACK tests
(https://github.com/OpenMathLib/OpenBLAS/issues/4282)

This change makes casum.c as similar as possible as zasum.c,
because zasum.c does this correctly.