libc: minimal: add qsort routine

[cfriedt]

Is your enhancement proposal related to a problem? Please describe.
It would be nice if the minimal libc supported qsort() within the stdlib area.

Implementation it via qsort_s() (C11) would probably make sense.

Since it's a global / standard C symbol, it could be enabled by default, as the linker would discard it if unused.

Describe the solution you'd like
A simple implementation of qsort_s() and qsort() via the former.

It might also make sense to define qsort() in terms of C11 generics so that e.g. an 8-bit, 16-bit, 32-bit, or 64-bit optimized version could be used when appropriate, and a generic memcpy() version could be used for objects beyond the size of normal integers. If so, then there would likely need to be a caveat, that any elements would be required to be aligned to their natural boundaries, if there is not one already.

Describe alternatives you've considered
There is a BSD-licensed implementation available from NuttX. I'm currently using it in Greybus for Zephyr, although I think it would be fine to write a less cryptic version.

Additional context

[JonBruchim]

I've actually opened a PR about this.

#29804

[cfriedt]

duplicates #28896