libc/stdlib: port illumos#15365: strtonumx() would be a useful companion to strtonum()

[rosenfeld_grumpf.hope-2000.org]

Summary

From the strtonum(3) manpage:

strtonum() is an OpenBSD extension. The existing alternatives, such as
atoi(3C) and strtol(3C), are either impossible or difficult to use
safely.

It would be useful if there was a new function that had the use and safety
properties of strtonum() but which understood base prefixes like the
strtol(3) family of functions does.

[kib]

This looks fine to me, but I prefer to have more eyes on it before is is engraved into the libc.

[ziaee]

Wow, thanks so much for sharing this with us!

lib/libc/stdlib/strtonum.3

194

We prefer to use version numbers here.

lib/libc/stdlib/strtonum.c

5

I'm not sure if it's necessary, but all our style guides use this.

[rosenfeld_grumpf.hope-2000.org]

lib/libc/stdlib/strtonum.3

194

illumos doesn't have versions or version numbers. If it helps I can try to find the exact date the commit went into illumos-gate.

lib/libc/stdlib/strtonum.c

5

It's the copyright of the original change, not mine. I'm not sure it would be well received by them if I changed it here?

[ziaee]

lib/libc/stdlib/strtonum.c

5

I don't know either, so I asked them. Hopefully they will come comment. It's so small, but I wanna get this kinda stuff right during import.

[emaste]

lib/libc/stdlib/strtonum.c

5

It's not necessary and if it's not in upstream; let's omit it. It's kind of silly that "Copyright (c)" is so prevalent, it'd be like writing "and &" or "% percent"