Resolve warnings on Windows

Appease the compiler by resolving some of the reported warnings,
including:

- Control paths that don't return.

- Potentially uninitialized variables.

- Unused local variables.

- Unreachable code.

- Type safety.

- Synchronize declarations with definitions for functions.

lib/roken/simple_exec_w32.c

@@ -80,7 +80,6 @@ wait_for_process_timed(pid_t pid, time_t (*func)(void *),
     hProcess = OpenProcess(SYNCHRONIZE, FALSE, pid);
 
     if (hProcess == NULL) {
-	DWORD dw = GetLastError();
         return SE_E_WAITPIDFAILED;
     }