Please help to fix outdated SUBST blocks

[Roland Illig <roland.illig%gmx.de@localhost>]

During the last 15 years, mk/subst.mk has been very forgiving. It just
skipped nonexistent files and files that didn't contain the expected
text. It produced some warnings, but these were easy enough to ignore.

This led to lots of outdated SUBST blocks. During the last month I
already found and fixed many of them (my bulk build with very strict
settings is at 15184/23223 packages). Fixing all the packages is
time-consuming for a single person.

If you'd like to help, just set SUBST_NOOP_OK=no in your mk.conf and
build packages as usual. And if a package fails to build, try to fix it
before I do. :)

To fix an issue, I typically take the relevant part of the configure.log
from the bulk build, paste that into a text editor, add to that the
SUBST block from the package Makefile and then inspect the files in
WRKSRC. That works pretty well.

I had hoped that I could simply switch to this strict mode after
branching 2020Q1, but that would have produced too much redundant work
on everyone. Having a few volunteers do this first seems like a better idea.

To see the progress, Jonathan has set up a bulk build named
"upstream-bulktest" whose results will appear on the pkgsrc-bulk mailing
list in a few days.

Thanks,
Roland