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_gettime/clock_gettime.c

@@ -1,4 +1,63 @@
-#ifdef __APPLE__
+/*
+ * Copyright (c), MM Weiss
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification,
+ * are permitted provided that the following conditions are met:
+ *
+ *     1. Redistributions of source code must retain the above copyright notice,
+ *     this list of conditions and the following disclaimer.
+ *
+ *     2. Redistributions in binary form must reproduce the above copyright notice,
+ *     this list of conditions and the following disclaimer in the documentation
+ *     and/or other materials provided with the distribution.
+ *
+ *     3. Neither the name of the MM Weiss nor the names of its contributors
+ *     may be used to endorse or promote products derived from this software without
+ *     specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
+ * SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
+ * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
+ * TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
+ * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/*
+ *  clock_gettime_stub.c
+ *  gcc -Wall -c clock_gettime_stub.c
+ *  posix realtime functions; MacOS user space glue
+ */
+
+/*  @comment
+ *  other possible implementation using intel builtin rdtsc
+ *  rdtsc-workaround: http://www.mcs.anl.gov/~kazutomo/rdtsc.html
+ *
+ *  we could get the ticks by doing this
+ *
+ *  __asm __volatile("mov %%ebx, %%esi\n\t"
+ *  		"cpuid\n\t"
+ *  		"xchg %%esi, %%ebx\n\t"
+ *  		"rdtsc"
+ *  		: "=a" (a),
+ *  		  "=d" (d)
+ * 	);
+ *  we could even replace our tricky sched_yield call by assembly code to get a better accurency,
+ *  anyway the following C stub will satisfy 99% of apps using posix clock_gettime call,
+ *  moreover, the setter version (clock_settime) could be easly written using mach primitives:
+ *  http://www.opensource.apple.com/source/xnu/xnu-${VERSION}/osfmk/man/ (clock_[set|get]_time)
+ *
+ *  hackers don't be crackers, don't you use a flush toilet?
+ *
+ *
+ *  @see draft: ./posix-realtime-stub/posix-realtime-stub.c
+ *
+ */
+
 
 #include "clock_gettime.h"
 #include <mach/clock.h>             // for clock_get_time
@@ -75,5 +134,3 @@ int clock_gettime(clockid_t clk_id, struct timespec *tp)
     }
     return retval;
 }
-
-#endif // __APPLE__