debian: sync with 4.21-1 package

debian: sync with 4.21-1 package

Versioned dependency on debhelper is not updated for backwards
compatibility.

* debian/changelog.in: Fix ancient changelog entries.
* debian/control (Build-Depends): Add dependency on libbluetooth-dev.
(Standards-Version): Update to 4.1.3.
(Vcs-Git, Vcs-Browser): Move from alioth to salsa.d.o.
(strace, strace-udeb) <Architecture>: Change to linux-any.
(strace64, strace-udeb) <Priority>: Change to optional.
* debian/rules: Use /usr/share/dpkg/architecture.mk instead of manually
setting build variables.
(configure): New target.
(build/Makefile, build-udeb/Makefile, build64/Makefile): Depend on it.
(binary-arch): Use build64/strace.1 for strace64 subpackage.
* debian/strace.manpages: Add build/ prefix.
* debian/strace64.manpages: Add build64/ prefix.