As the one who reported the issue in the glibc upstream tracker, I'm now of the opinion it's not a glibc bug, but rather issues with the individual packages that are now FTBFS. As far as I know, this is either a parser pretending to be GCC without implementing all the GCC features (e.g. aspectc++), and/or a compiler targetting another platform while still using the system headers (e.g. rocm-hipamd).
- Bug#1070668: glibc: packages FTBFS caused by vector math li... Aurelien Jarno
- Bug#1070668: Processed: glibc: packages FTBFS caused b... Simon Chopin
- Bug#1070668: Processed: glibc: packages FTBFS caus... Aurelien Jarno