My feeling is that glibc upstream will not want to care about cross qemu situations. I would prefer to report it to the Ubuntu cross-tools maintainers: The package libc6-<cpu>-cross contains the file /usr/<cpu>-linux-gnu/lib/libc.so.6; they could surely add the symlink for /usr/<cpu>-linux-gnu/etc/ld.so.cache as well.
My feeling is that glibc upstream will not want to care about cross qemu situations. I would prefer to report it to the Ubuntu cross-tools maintainers: The package libc6-<cpu>-cross contains the file /usr/<cpu> -linux- gnu/lib/ libc.so. 6; they could surely add the symlink for /usr/<cpu> -linux- gnu/etc/ ld.so.cache as well.