* 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.

Unlike [dcz]scal, sscal still used the original GotoBLAS SSE code from scal_sse.S.
This code follows dscal as closely as possible, except for the inc_x > 1 code
for which a plain C loop is used much like the one in cscal.c, instead of an
adaptation of the SSE2 asm code of dscal.c (I tried but the performance wasn't
better than the plain C loop).

Using 256-bit registers in dscal makes this microkernel consistent with
cscal and zscal, and generally doubles performance if the vector fits in
L1 cache.

These are as similar to dscal_microk_skylakex-2.c as possible
for consistency.

Note that before this change SKYLAKEX+ uses generic C functions for
cscal/zscal via commit 2271c350 from #2610 (which is masked by
commit 086d87a30). However now #3799 disables FMAs (in turn enabled
by `-march=skylake-avx512`) in the plain C code which fixes excessive
LAPACK test failures more nicely.