removed os_compat.h

Only include headers which are really needed.  os_compat.h aimed to
make MPD easily portable, but was never actually made portable.

src/compress.c

@@ -20,10 +20,12 @@
  *
  */
 
-#include "os_compat.h"
 #include "compress.h"
 #include "utils.h"
 
+#include <stdint.h>
+#include <string.h>
+
 #ifdef USE_X
 #include <X11/Xlib.h>
 #include <X11/Xutil.h>