ldlibs: Try loading Clear Linux ld.so cache
Clear Linux patches glibc to put ld.so.cache in /var/cache/ldconfig/ to meet their goal of /etc being initially empty and reserved for the sysadmin. We can handle this just like the conventional path: it doesn't need to be architecture-specific.
Partially addresses https://github.com/ValveSoftware/steam-runtime/issues/345