FFI: Fix FOLD rules for int64_t comparisons.

Thanks to Peter Cawley.

src/lj_opt_fold.c

@@ -444,14 +444,14 @@ LJFOLDF(kfold_int64comp)
 #if LJ_HASFFI
   uint64_t a = ir_k64(fleft)->u64, b = ir_k64(fright)->u64;
   switch ((IROp)fins->o) {
-  case IR_LT: return CONDFOLD(a < b);
-  case IR_GE: return CONDFOLD(a >= b);
-  case IR_LE: return CONDFOLD(a <= b);
-  case IR_GT: return CONDFOLD(a > b);
-  case IR_ULT: return CONDFOLD((uint64_t)a < (uint64_t)b);
-  case IR_UGE: return CONDFOLD((uint64_t)a >= (uint64_t)b);
-  case IR_ULE: return CONDFOLD((uint64_t)a <= (uint64_t)b);
-  case IR_UGT: return CONDFOLD((uint64_t)a > (uint64_t)b);
+  case IR_LT: return CONDFOLD((int64_t)a < (int64_t)b);
+  case IR_GE: return CONDFOLD((int64_t)a >= (int64_t)b);
+  case IR_LE: return CONDFOLD((int64_t)a <= (int64_t)b);
+  case IR_GT: return CONDFOLD((int64_t)a > (int64_t)b);
+  case IR_ULT: return CONDFOLD(a < b);
+  case IR_UGE: return CONDFOLD(a >= b);
+  case IR_ULE: return CONDFOLD(a <= b);
+  case IR_UGT: return CONDFOLD(a > b);
   default: lua_assert(0); return FAILFOLD;
   }
 #else