Bug#666772: apt cross-build-dep handling should be liberal with Arch: all packages

[Nick Leverton <nick@leverton.org>]

Hi,

TL;DR  Dpkg does the useful thing, apt-get build-dep doesn't.

I've just been getting a setup working for Debian cross-building.
At work I use OpenEmbedded which is a time consuming pain in
the neck.  I hope to get to a work flow that can replace crappy
embedded vendor toolchains but for the moment I'm following Wookie's
recipe at https://wiki.debian.org/CrossToolchains which complements
his talk at Cambridge mini-debconf.  To the extent that there is any
maintainer-supported user-level cross building support in Debian, this
seems to be it from my reading.

However this bug is a significant blocker to that work process.
Several of the basic Priority Essential packages won't cross-build
with target != host because of the current bug.

dpkg-checkbuilddeps already allows Arch:all Multi-Arch:none packages to
satisfy build-depends.  I've built apt with the patch here and this allows
"apt-get build-dep" to do the useful thing also.  Both the failures in
the attached log go away with this patch to apt.

Please therefore can this patch be applied and released ?

Many thanks

Nick Leverton

[jessie-amd64-sbuild-tar: leveret@warren ~/src/apt-1.0.9.3]$ apt-get -s build-dep apt dpkg -a armhf   
Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Build-Depends dependency for apt cannot be satisfied because the package docbook-xml cannot be found
[jessie-amd64-sbuild-tar: leveret@warren ~/src/apt-1.0.9.3]$ apt-get -s build-dep  dpkg -a armhf 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Build-Depends dependency for dpkg cannot be satisfied because the package libtimedate-perl cannot be found