while at beta3, overriding get_entropy64.

there are not (yet) real userland interface however there are nice templatized C++ ones,
a little performance gain from it.

Author: devnexen

src/pal/pal_haiku.h

@@ -6,6 +6,8 @@
 
 #  include <sys/mman.h>
 
+extern uint64_t secure_get_random();
+
 namespace snmalloc
 {
   /**
@@ -43,6 +45,11 @@ namespace snmalloc
       mprotect(p, size, PROT_NONE);
 #  endif
     }
+
+    static uint64_t get_entropy64()
+    {
+      return secure_get_random();
+    }
   };
 } // namespace snmalloc
 #endif