No talking in this bug.
Typical fixes are to be described at https://wiki.gentoo.org/wiki/Project:Toolchain#Porting_notes
For Postgres databases using language and region-sensitive collations, which tend to be the default nowadays, it means that certain strings might sort differently after this upgrade. A critical consequence is that indexes that depend on such collations must be rebuilt immediately after the upgrade. Servers in WAL-based/streaming replication setups should also be upgraded together since a standby must run the same libc/locales as its primary.