libc: minimal: add strerror() function

[cfriedt]

Is your enhancement proposal related to a problem? Please describe.
An issue with portability is the lack of a strerror() function.

However, it is understandable why the function is not included (the string table increases ROM footprint and we want to keep Zephyr small).

It's an annoyance to have to #ifdef-out sections of 3rd-party code that rely on its presence.

Describe the solution you'd like
A functional strerror() with a Kconfig option to enable the string error table.

Describe alternatives you've considered
#ifdef-ing out code in 3rd-party libraries ad-infinitum.

Additional context
Useful for perror()