invalid gdk-pixbuf-thumbnailer path assumption in build system
Issue Summary
The gdk-pixbuf-thumbnailer command path is assumed by the build system to be in its bindir output (https://gitlab.gnome.org/GNOME/librsvg/-/blob/main/gdk-pixbuf-loader/librsvg.thumbnailer.in#L2), which is a fragile assumption (broken on NixOS and Guix and possibly in snaps, etc.). It was patched by NixOS here: https://github.com/NixOS/nixpkgs/pull/29984 but not reported.
Ideas for a fix: detect the location of gdk-pixbuf at build time (via pkg-config) and use that if available, or provide a configure flag to set its path directly.