Contents of haddock-prologue are not output even with -v3

[phadej]

I have no idea what are its contents, and as there is no way to preserve temporary files (see #11234) debugging haddock invocations is unnecessarily more difficult.

[ffaf1]

Is this still relevant after #11234 was closed?

[phadej]

Yes. I still have no idea what are the contents of the prologue. -v3 ought to print that too if it prints e.g. contents of response files.