Uncaught [Unix.Unix_error(Unix.ECHILD, "waitpid", "")] when using why3

[fblanqui]

11:41 ~/src/lambdapi (master) \rm tests/OK/*.lpo
11:41 ~/src/lambdapi (master) dune exec -- lambdapi check -w -c tests/OK/why3_quantifiers.lp tests/OK/logic.lp tests/OK/bool.lp tests/OK/nat.lp
Loading "/home/blanqui/src/lambdapi/tests/OK/why3_quantifiers.lp" ...
Loading "/home/blanqui/src/lambdapi/tests/OK/logic.lp" ...
Loading "/home/blanqui/src/lambdapi/tests/OK/bool.lp" ...
Loading "/home/blanqui/src/lambdapi/tests/OK/nat.lp" ...
Uncaught [Unix.Unix_error(Unix.ECHILD, "waitpid", "")].
Loading "/home/blanqui/src/lambdapi/tests/OK/logic.lp" ...
Loading "/home/blanqui/src/lambdapi/tests/OK/bool.lp" ...
Loading "/home/blanqui/src/lambdapi/tests/OK/nat.lp" ...
Loading "/home/blanqui/src/lambdapi/tests/OK/bool.lp" ...
Loading "/home/blanqui/src/lambdapi/tests/OK/nat.lp" ...
Loading "/home/blanqui/src/lambdapi/tests/OK/bool.lp" ...

[fblanqui]

11:58 ~/src/lambdapi (master) dune exec -- lambdapi check -c tests/OK/why3_quantifiers.lp
Loading "/home/blanqui/src/lambdapi/tests/OK/why3_quantifiers.lp" ...
Loading "/home/blanqui/src/lambdapi/tests/OK/logic.lp" ...
Loading "/home/blanqui/src/lambdapi/tests/OK/bool.lp" ...
Loading "/home/blanqui/src/lambdapi/tests/OK/nat.lp" ...
Uncaught [Unix.Unix_error(Unix.ECHILD, "waitpid", "")].

[fblanqui]

There is no problem if we remove the option -c. So it must be related to the writing of lpo files.