Releases 7.0 and 8.0 brought some bug fixes and perf improvements when working with UTF-8 locales, but the main reason why I'm asking to update it is a possibility of building GDB with system-wide readline instead of bundled library. Our readline is too old for GDB 10.1, and I'm not submitting update myself since it's a part of system.base.
Tarball: https://ftp.gnu.org/gnu/readline/readline-8.0.tar.gz
Patches: https://ftp.gnu.org/gnu/readline/readline-8.0-patches/