On Linux support PR_SET_PTHREADSIG

[da-x]

[hniksic]

Thanks for the PR. The feature seems quite specific - could you please describe the use case for it?

I'm wondering if it might make more sense to enable some sort of post-fork hook to allow user-provided code to invoke calls like libc::prctl(libc::PR_SET_PDEATHSIG, signal).