JLS says:
The body of a compact constructor declaration must satisfy all of the following conditions, or a compile-time error occurs:

The body must not contain an explicit constructor invocation (8.8.7.1).

But in JEP-401 EA2 this code is accepted:

Welcome to JShell -- Version 26-jep401ea2
| For an introduction type: /help intro
 
jshell> record Record(int x) {
   ...> public Record {
   ...> super();
   ...> }
   ...> }
| created record Record