Merge branch 'bugfix/conditionals-with-function-calls' into 'master'

ref:extensions/dune-codegen This does not work if the predicate contains a
function call (you cannot infer the possible return values at codegen time).

See merge request [extensions/dune-codegen!372]

  [extensions/dune-codegen!372]: gitlab.dune-project.org/extensions/dune-codegen/merge_requests/372