Use fewer header files

Removing some includes to reduce the code that is dragged in.

src/pal/pal_apple.h

@@ -5,10 +5,11 @@
 #  include "../mem/allocconfig.h"
 
 #  include <pthread.h>
-#  include <stdio.h>
 #  include <strings.h>
 #  include <sys/mman.h>
 
+int puts ( const char * str );
+
 namespace snmalloc
 {
   /**

src/pal/pal_freebsd.h

@@ -4,7 +4,6 @@
 #  include "../ds/bits.h"
 #  include "../mem/allocconfig.h"
 
-#  include <pthread.h>
 #  include <stdio.h>
 #  include <strings.h>
 #  include <sys/mman.h>

src/pal/pal_linux.h

@@ -4,10 +4,11 @@
 #  include "../ds/bits.h"
 #  include "../mem/allocconfig.h"
 
-#  include <stdio.h>
 #  include <string.h>
 #  include <sys/mman.h>
 
+int puts ( const char * str );
+
 namespace snmalloc
 {
   class PALLinux