flex is no longer M-A:foreign

[Helmut Grohne <helmut@subdivi.de>]

Hi,

I am seeking consensus on what to do about flex. Until recently, it
carried Multi-Arch: foreign. That was wrong (#761449) as it exposes
libfl-dev and thus the architecture of libfl-dev. Since libfl-dev was
only installed for the build architecture, this broke the build of e.g.
pam.

Now Manoj fixed that bug by removing Multi-Arch: foreign despite the
presence of a patch. The patch is arguably intrusive as it renames flex
to flex-bin and libfl-dev to flex, but from an interface pov, nothing
changes (except for picking the "right" architecture libraries). The new
flex package provides libfl-dev and its new dependency on flex-bin
causes flex binary to be present as expected.

The current state is that a build dependency on flex means to install
the host architecture flex (with the host architecture flex libraries),
but we cannot run host architecture code, so all builds running flex
fail.

How do we want to handle this? I see two ways:
1) Apply my patch in the above bug report.
2) Change all dependencies on flex into "flex:native, libfl-dev".

The second option requires a MBF involving 500 source packages and a
one-digit number of binary package depends.

There also is an intermediate option where flex drops its dependency on
libfl-dev. In that case, it can become Multi-Arch: foreign again. Since
not every of those 500 source packages use libfl-dev, this would cause
fewer bugs. It still incurs the MBF.

Given that my favourite option was turned down by the maintainer, the
next available fix unfortunately looks like a MBF to me. I would very
much like to avoid this route. So unless someone has a better idea, I'll
go ahead and announce the MBF to d-devel.

Helmut