add HEAP_PAGE_SIZE to internal constants

gc.c

@@ -12604,6 +12604,7 @@ Init_GC(void)
     rb_hash_aset(gc_constants, ID2SYM(rb_intern("HEAP_PAGE_OBJ_LIMIT")), SIZET2NUM(HEAP_PAGE_OBJ_LIMIT));
     rb_hash_aset(gc_constants, ID2SYM(rb_intern("HEAP_PAGE_BITMAP_SIZE")), SIZET2NUM(HEAP_PAGE_BITMAP_SIZE));
     rb_hash_aset(gc_constants, ID2SYM(rb_intern("HEAP_PAGE_BITMAP_PLANES")), SIZET2NUM(HEAP_PAGE_BITMAP_PLANES));
+    rb_hash_aset(gc_constants, ID2SYM(rb_intern("HEAP_PAGE_SIZE")), SIZET2NUM(HEAP_PAGE_SIZE));
     OBJ_FREEZE(gc_constants);
     /* internal constants */
     rb_define_const(rb_mGC, "INTERNAL_CONSTANTS", gc_constants);