FFI: Check for __new metamethod when calling a constructor.

src/lj_obj.h

@@ -437,6 +437,12 @@ enum {
 #define setvmstate(g, st)	((g)->vmstate = ~LJ_VMST_##st)
 
 /* Metamethods. ORDER MM */
+#ifdef LJ_HASFFI
+#define MMDEF_FFI(_) _(new)
+#else
+#define MMDEF_FFI(_)
+#endif
+
 #ifdef LUAJIT_ENABLE_LUA52COMPAT
 #define MMDEF_52(_) _(pairs) _(ipairs)
 #else
@@ -450,7 +456,7 @@ enum {
   /* The following must be in ORDER ARITH. */ \
   _(add) _(sub) _(mul) _(div) _(mod) _(pow) _(unm) \
   /* The following are used in the standard libraries. */ \
-  _(metatable) _(tostring) MMDEF_52(_)
+  _(metatable) _(tostring) MMDEF_FFI(_) MMDEF_52(_)
 
 typedef enum {
 #define MMENUM(name)	MM_##name,