With gcc 15 building OCaml < 5.1.0 is broken due to the build error below. The commit that fixes this issue in 5.1.0 appears to be here: 8db1817 In file included from ...

(cond ((null? rest) (make-let-internal-def args vals rest)) ((definition? (car rest)) (scan (cdr rest) (append-to-list (definition-variable (car rest)) args) (append ...