From Fedora Project Wiki

gdk-pixbuf loaders

gdk-pixbuf is a library that is part of the gdk-pixbuf2 package. It is for loading images in various formats in GNOME. gdk-pixbuf can be extended by implementing loaders for image formats in loadable modules. These loadable modules have to be installed in %{_libdir}/gdk-pixbuf-2.0/2.10.0/loaders. To avoid opening all modules in that directory unnecessarily, gdk-pixbuf maintains a cache with information about the available modules in the text file %{_libdir}/gdk-pixbuf-2.0/2.10.0/loaders.cache. This cache file needs to be updated when the set of installed modules changes, by calling the gdk-pixbuf-query-loaders binary. Multilib considerations force us to install the binary in -32 and -64 variants.

The proposed scriptlets to maintain the cache file are:

gdk-pixbuf-query-loaders-%{__isa_bits} --update-cache || :

gdk-pixbuf-query-loaders-%{__isa_bits} --update-cache || :

Note the use of %{__isa_bits}, which is an rpm macro that expands to either 32 or 64, depending on the architecture of the package.

In order to ensure that gdk-pixbuf-query-loaders is available when the scriptlets are run, add Requires as necessary:

<pre Requires(postun): gdk-pixbuf2 Requires(posttrans): gdk-pixbuf2