OS X compatibility cleanups.

Reattach the licenses for the compat stuff to the source.
Only build/link the compat stuff when it's needed.
Rename compat/util.h so it's not confused with util.h.
Move all the platform specific defines inside compat/compat.h.

compat/clock_nanosleep/clock_nanosleep.c

@@ -2,7 +2,22 @@
  * clock_nanosleep.c - clock_nanosleep() replacement
  */
 
-#ifdef __APPLE__
+/***********************************************************************
+ *  Copyright © 2006 Rémi Denis-Courmont.                              *
+ *  This program is free software; you can redistribute and/or modify  *
+ *  it under the terms of the GNU General Public License as published  *
+ *  by the Free Software Foundation; version 2 of the license, or (at  *
+ *  your option) any later version.                                    *
+ *                                                                     *
+ *  This program is distributed in the hope that it will be useful,    *
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of     *
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.               *
+ *  See the GNU General Public License for more details.               *
+ *                                                                     *
+ *  You should have received a copy of the GNU General Public License  *
+ *  along with this program; if not, you can get it from:              *
+ *  http://www.gnu.org/copyleft/gpl.html                               *
+ ***********************************************************************/
 
 #include "clock_nanosleep.h"
 #include <errno.h>                           // for errno, EINVAL
@@ -45,5 +60,3 @@ int clock_nanosleep(clockid_t id, int flags, const struct timespec *ts,
 
     return ret ? errno : 0;
 }
-
-#endif // __APPLE__

compat/clock_nanosleep/clock_nanosleep.h

@@ -1,5 +1,3 @@
-#ifdef __APPLE__
-
 #ifndef CLOCK_NANOSLEEP_H
 #define CLOCK_NANOSLEEP_H
 
@@ -24,4 +22,3 @@ int clock_nanosleep (clockid_t id, int flags, const struct timespec *ts,
                      struct timespec *ots);
 
 #endif //CLOCK_NANOSLEEP_H
-#endif // __APPLE__