gitg won't run if libdir is overriden
If you build gitg with something like
--libdir=lib/gitg (which expands to
/usr/lib/gitg/ when built as a distro package), gitg won't run.
gitg: error while loading shared libraries: libgitg-ext-1.0.so.0: cannot open shared object file: No such file or directory
This is a regression compared to the autotools build. This hit Debian with 3.30.1 since we hadn't yet switched to autotools and we prefer to install these libraries to an app-specific directory since they are app-specific.