This is just a warning that soon, I'd like to enable --slow ./validate
What does this mean? It means that builds will take longer, but GHC
will be tested much more thoroughly with each commit and with each
patch that's submitted.
Unfortunately, the bad news is that we've been pretty sloppy about
making sure the --slow configuration always works... last I tried it
(admittedly a little while ago) there were quite a few extra failures.
However, this is just a pre-emptive warning that things may take
longer, and a few things may break more soon.
Particularly, there's now the chance Harbormaster will see failures
that you did not see before! (for example, if you changed the code
generator and broke the profiling build). But that's probably a good
thing, since you can defer to checking slow tests afterwords.