When --host-arch is passed into mk-build-deps, the generated package's
dependencies always use the specified architecture. However, this behavior
causes issues when a build dependency has the "all" architecture, since mk-
build-deps will try to install that package for an architecture which doesn't
exist.

To reproduce:
$ git clone --depth=1 https://salsa.debian.org/xorg-team/lib/mesa-amber.git
$ cd mesa-amber
$ mk-build-deps --host-arch arm64
$ apt-get install -y ./*.deb
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Note, selecting 'mesa-amber-cross-build-deps:arm64' instead of './mesa-amber-
cross-build-deps_21.3.9-1_arm64.deb'
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 mesa-amber-cross-build-deps:arm64 : Depends: python3:arm64 but it is not going
to be installed
                                     Depends: python3-mako:arm64 but it is not
installable

In this example, mk-build-deps tries to install python3-mako:arm64, which
doens't exist. The correct package would be python3-mako:all.
--- /etc/devscripts.conf ---
Empty.

--- ~/.devscripts ---
Not present