Preparing for pkgsrc-2026Q1 - avoid problematic changes

Hi all,

Per the instructions in https://pkgsrc.org/quarterly/ we should now
start the first stage of preparing for the new branch.

The following changes will now require approval:

- any package always needing approval (boost, gmake, qt5) - the
  standard answer will be wait until after the branch

- any change in mk that is intended to result in build failures
  (typically for things that were warnings before)

- clang/llvm (New versions almost always are backwards incompatible.)

- poppler* (frequent API changes)

- Any package with a history of a troubled update in the last 3 years:
  - glib2
  - py-sip6


Changes to other packages are OK and don't require approval.

Additional restrictions will be added and communicated on March 1
(they're also documented in the quarterly URL above).
I intend to start a pkgsrc freeze around March 14/15.

Thanks!