'make distcheck' failure

[Bruno Haible]

Today, on the master branch, in the 'jitter' directory, there is a failure
of "make distcheck":

make[5]: *** No rule to make target 
'machine/dummy--minimal-threading/jitter/machine/jitter-machine-assembly.S', 
needed by 'distdir-am'.  Stop.

Found by the CI, at https://gitlab.com/gnu-poke/ci-distcheck/-/jobs/3642524958

Same as already reported in 
https://lists.gnu.org/archive/html/poke-devel/2022-02/msg00035.html.

Bruno