daemon: Moved empty Windows version functions to header file

On Windows only daemonize_close_stdin() function does
something.  Other functions are either empty or generate an
error.  Those have been moved to header file and declared
static inline so compiler can remove the call all together.

src/daemon.h

@@ -22,18 +22,36 @@
 
 #include <stdbool.h>
 
+#ifndef WIN32
 void
 daemonize_init(const char *user, const char *group, const char *pidfile);
+#else
+static inline void
+daemonize_init(const char *user, const char *group, const char *pidfile)
+{ (void)user; (void)group; (void)pidfile; }
+#endif
 
+#ifndef WIN32
 void
 daemonize_finish(void);
+#else
+static inline void
+daemonize_finish(void)
+{ /* nop */ }
+#endif
 
 /**
  * Kill the MPD which is currently running, pid determined from the
  * pid file.
  */
+#ifndef WIN32
 void
 daemonize_kill(void);
+#else
+static inline void
+daemonize_kill(void)
+{ g_error("--kill is not available on WIN32"); }
+#endif
 
 /**
  * Close stdin (fd 0) and re-open it as /dev/null.
@@ -44,10 +62,22 @@ daemonize_close_stdin(void);
 /**
  * Change to the configured Unix user.
  */
+#ifndef WIN32
 void
 daemonize_set_user(void);
+#else
+static inline void
+daemonize_set_user(void)
+{ /* nop */ }
+#endif
 
+#ifndef WIN32
 void
 daemonize(bool detach);
+#else
+static inline void
+daemonize(bool detach)
+{ (void)detach; }
+#endif
 
 #endif