[Bug target/44002] need to #include unistd.h for pid_t on alpha-dec-vms

[egallager at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=44002

--- Comment #5 from Eric Gallager <egallager at gcc dot gnu.org> ---
(In reply to Jay from comment #4)
> Incorrect bug.

Correct place was bug 84628 comment #6, for any confused onlookers