Drop dependency on LGPL-3 libdw for better backtraces

The libdw library is used to get better backtraces, but it is
dual-licensed GPL-2 OR LGPL-3 which means that it either:

* restricts all users of GStreamers to be GPL-2
* requires users to be subject to the LGPL-3 provisions

Neither is acceptable for Apertis, so make sure that libgstreamer1.0-0
does not link to libdw1.

Signed-off-by: Emanuele Aina <emanuele.aina@collabora.com>

debian/control

@@ -15,7 +15,7 @@ Build-Depends: debhelper,
                libgmp-dev | libgmp3-dev,
                libgsl-dev | libgsl0-dev,
                libunwind-dev [i386 amd64 armel armhf arm64 powerpc ppc64 ppc64el mipsel mips64el],
-               libdw-dev [i386 amd64 armel armhf arm64 powerpc ppc64 ppc64el mipsel mips64el],
+#               libdw-dev [i386 amd64 armel armhf arm64 powerpc ppc64 ppc64el mipsel mips64el], # LGPL-3
                bison (>= 1:2.4),
                flex (>= 2.5.34),
                libgirepository1.0-dev (>= 0.9.12-4~),
@@ -25,6 +25,7 @@ Build-Depends: debhelper,
                bash-completion,
                libcap2-bin [linux-any],
                libcap-dev [linux-any]
+Build-Conflicts: libdw-dev
 Standards-Version: 4.5.0
 Vcs-Git: https://salsa.debian.org/gstreamer-team/gstreamer1.0.git
 Vcs-Browser: https://salsa.debian.org/gstreamer-team/gstreamer1.0/