Re: [PATCH 2/4] vircommand: Isolate FD dir parsing into a separate function

So far, virCommandMassCloseGetFDsLinux() opens "/proc/self/fd", iterates over it marking opened FDs in @fds bitmap. Well, we can do the same on other systems (with altered path), like MacOS or FreeBSD. Therefore, isolate dir iteration into a separate function that accepts dir path as an argument. Unfortunately, this function might be unused on some systems (e.g. mingw), therefore mark it as such.