Looking at the build log in the linked Debian issue, there is an argument setting -std=c++11. It seems as though an implicit inclusion of <cstdint> had been provided by libstdc++ in the past and was removed as of GCC 15.
it would be nice if g++ had an --implicit-includes=[foo,bar] option that would make it easier for a distro to shotgun fix such incompatibilities with CXXFLAGS rather than doing real work.