maint: shorten https://lists.gnu.org/archive/html/... links

maint: shorten https://lists.gnu.org/archive/html/... links

Each /archive/html/ part can be replace with /r/.
Run this to induce the change:
git grep -l archive/html|xargs perl -pi -e 's,/archive/html/,/r/,g'
* TODO: Perform that substitution.
* bootstrap: Likewise.
* src/sort.c (sequential_sort): Likewise.
* src/tail.c (tail_file): Likewise.
* tests/misc/sort-merge-fdlimit.sh: Likewise.
* tests/misc/stty-row-col.sh: Likewise.
* tests/misc/unexpand.pl: Likewise.
* tests/rm/readdir-bug.sh: Likewise.
* tests/tail-2/inotify-rotate.sh: Likewise.