Enhancement request: `--dry-run` flag for `runtest`

[Eric Gallager]

Many command-line utilities have a "--dry-run" flag to print what
would be done by running them without actually performing any changes.
I was thinking one would be particularly useful for running the GCC
testsuite (to put in RUNTESTFLAGS), since it is quite large and
running it can take quite a long time, yet sometimes there are reasons
to run it besides actually running it (e.g., getting a list of tests
run). For example, https://gcc.gnu.org/install/test.html says: "To get
a list of the possible *.exp files, pipe the output of ‘make check’
into a file and look at the ‘Running … .exp’ lines," which is
something that I thought being able to do "RUNTEST_FLAGS=--dry-run"
would be useful for. Let me know if you need me to find specific
examples of software that already has the kind of "--dry-run" flag I'm
thinking of.
Thanks,
Eric Gallager