can't call foreign function `__libc_current_sigrtmin`

[dead-claudia]

__libc_current_sigrtmax is present (and so I can use libc::SIGRTMAX() without issue), but not __libc_current_sigrtmin for some reason (preventing me from using libc::SIGRTMIN()).

I could easily shim this to 35 for practical testing purposes (kernel starts at 32, glibc reserves 3 for its threading library), but it'd be nice to not have to hack that in.

[RalfJung]

Yeah that should be easy to add in Miri.