Rebased patches and some sorting in APKBUILD

Make safekeep work with rdiff-backup 2.0.5

Ref rdiff-backup issue #480

khtml is present again

This reverts commit ff0f7f79.

This reverts commit 5f136fa1.

firefox-esr is currently broken with rust >= 1.47

See !13787

This reverts commit 3c2ea94e.

This commit has not been tested locally, but firefox is completely
broken at the moment anyhow so let's just see if this fixes it...

OK Ariadne@

10b83865 (Revert "main/gc: disable-parallel-mark build option",
2020-10-30) also decreased pkgrel. For systems that already had -r2,
they won't be downgraded again, unless they provide `--available`.

Let's bump pkgrel to 3 so that those systems get the reverted version
again.

The value of O_LARGEFILE is changed on x86_64. While it makes
functionally no change, the rebuild is needed for seccomp to allow
this bit being set.