Add multiarch metadata to gir1.2-gstreamer-1.0

[Derek Gasaway]

Release: Artful Aardvark 17.10
Package version: 1.12.3-1

I modified the debian/gir1.2-gstreamer-1.0.install file to put its girepository-1.0 files under the architecture-dependent directory, by removing the target specifier (usr/lib). As far as I can tell, the non-architecture specific files are just doc files, and should be the same on other architectures. I then successfully installed the modified package and imported Gst using python3-gi. Changing the install directory plus adding Multi-Arch: same to gir1.2-gstreamer-1.0 should make it multiarch-compatible.

It's also likely that libgstreamer1.0-dev could also be Multi-Arch: same if it weren't for the binaries in the package, although I don't know an easy solution to that - for instance gst-codec-info-1.0 loads plugins dynamically, which fails (with an accurate warning message) if used on the wrong architecture. Renaming it/giving it an architecture-dependent path (e.g. x86_64-linux-gnu-gcc) would probably break backwards compatibility, and there are about 20 rdepends for libgstreamer1.0-dev, which as gst-codec-info-1.0 and dh_gstscancodecs seem designed for use by packagers are probably the only places to check for usage.