pkg: Use a global buffer for local ABI string

[jhb]

Summary

Otherwise c[ABI].val can point to a no-longer-valid on-stack buffer
after config_init returns.

Reported by: GCC 13 -Wdangling-pointer

[emaste]

OK with me, or we could have pkg_get_myabi asprintf it?

[jhb]

In D42583#971581, @emaste wrote:

OK with me, or we could have pkg_get_myabi asprintf it?

I don't know that we really need that extra complexity TBH. But alternatively, yes, I would make pkg_get_myabi() return an allocated string that the caller has to manage the lifetime of.

[jhb]

Actually, I like the asprintf version better, so I will upload that in a bit.

[emaste]

Sorry for making more work for you :)