More work on the scheduler for windows

- Get a rump derivation goal: hook instance will come later, local
  derivation goal will come after that.

- Start cleaning up the channel / waiting code with an abstraction.

src/libutil/processes.hh

@@ -118,8 +118,6 @@ public:
     { }
 };
 
-#ifndef _WIN32
-
 /**
  * Convert the exit status of a child as returned by wait() into an
  * error string.
@@ -128,6 +126,4 @@ std::string statusToString(int status);
 
 bool statusOk(int status);
 
-#endif
-
 }