bug#41404: Crash "Too many root sets" when executing code from stdin in elisp mode

[Vasilij Schneidermann]

The attached reproducer script requires Emacs and Guile.  When running it, the
REPL prints out many lines, the last ones being:

    $1884 = #f
    $1885 = #f
    $1886 = #f
    $1887 = #f
    $1888 = #f
    $1889 = #f
    $1890 = #f
    $1891 = #f
    $1892 = #f
    Too many root sets
    ./repro.sh: line 11:  2014 Aborted (core dumped) guile --language=elisp < 
elisp-spec.el

This happens both for Guile 2.2.6 on Arch and Guile 3.0.2 on Debian Sid,
launched with `docker run --rm -i -t debian:sid bash`.

repro.sh
Description: Bourne shell script

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