Relax the requirements for the tests, to fall back on the bytecode
version when the native version is not available. Otherwise the tests
will fail on bytecode-only architectures.
Rewrite a test to shorten the lexical scope of the string it builds
because, in the bytecode backend, a variable is deemed live at least as
long as its lexical scope.
Reference: https://github.com/ocaml/ocaml/pull/10071