[mono][interp] Add missing sign extend

Fix passing of i4 to wrapper accepting native int. The wrapper no longer does the sign extend in order to not lose high bits of native int.

src/mono/mono/mini/method-to-ir.c

@@ -4453,8 +4453,18 @@ mini_emit_array_store (MonoCompile *cfg, MonoClass *klass, MonoInst **sp, gboole
 		if (sp [2]->type != STACK_OBJ)
 			return NULL;
 
+		MonoInst *index_ins = sp [1];
+#if SIZEOF_REGISTER == 8
+		if (sp [1]->type == STACK_I4) {
+			// stelemref wrapper recevies index as native int, sign extend it
+			guint32 dreg = alloc_preg (cfg);
+			guint32 sreg = index_ins->dreg;
+			EMIT_NEW_UNALU (cfg, index_ins, OP_SEXT_I4, dreg, sreg);
+		}
+#endif
+
 		iargs [2] = sp [2];
-		iargs [1] = sp [1];
+		iargs [1] = index_ins;
 		iargs [0] = sp [0];
 
 		MonoClass *array_class = sp [0]->klass;