Fix another test impacted by #157364.
On Windows, `GetComputerNameA()`, which is what this ends up calling,
takes an `LPDWORD`, but we were handing it an `int*`; fix this by
declaring it as a `DWORD` instead.
Add a missing <process.h> include for _getpid. Don't typedef the
pid_t type on mingw, as mingw headers already provide a typedef for
it.
Differential Revision: https://reviews.llvm.org/D137745