Bug#846427: freebsd-buildutils: add libfl-dev to Build-Depends

[Helmut Grohne <helmut@subdivi.de>]

Source: freebsd-buildutils
Severity: important
User: helmutg@debian.org
Usertags: libfldep

freebsd-buildutils will soon fail to build from source, beause flex
drops its dependency on libfl-dev. Since freebsd-buildutils uses
parts of libfl-dev (e.g. libl.a, libfl.a or FlexLexer.h), it should
add libfl-dev to its Build-Depends. This change was previously
announced[1] to debian-devel in accordance with DevRef 7.1.1. Please
add the missing dependency.

Helmut

[1] https://lists.debian.org/debian-devel/2016/03/msg00162.html