xo-imgui: clang compiler nits

include/xo/alloc/GC.hpp

@@ -119,6 +119,8 @@ namespace xo {
          **/
         class GcCopyCallback {
         public:
+            virtual ~GcCopyCallback() = default;
+
             virtual void notify_gc_copy(std::size_t z, const void * src_addr, const void * dest_addr,
                                         generation src_gen, generation dest_gen) = 0;
             /** invoked when added to callback set (i.e. @ref GC::GcCopyCallbackSet) **/

include/xo/alloc/ObjectStatistics.hpp

@@ -56,7 +56,8 @@ namespace xo {
          *
          *  Passed to @ref Object::deep_move for example
          **/
-        struct ObjectStatistics {
+        class ObjectStatistics {
+        public:
             void display(std::ostream & os) const;
 
             /** per-object-type statistics, indexed by TypeId **/

src/alloc/ArenaAlloc.cpp

@@ -9,6 +9,7 @@
 #include "xo/indentlog/scope.hpp"
 #include "xo/indentlog/print/tag.hpp"
 #include <sys/mman.h>
+#include <unistd.h> // for getpagesize() on OSX
 #include <cassert>
 
 namespace xo {