Created attachment 701046 [details] build.log build.log attached. Works on a system with glib-2.66.7.
The errors are narrowing conversion errors. They don't appear to be related to glib. In any case, I think https://salsa.debian.org/wpanlener-guest/mangler/-/blob/master/debian/patches/fix_ftbfs_narrowing_conversion.patch will fix the issue.
The bug has been closed via the following commit(s): https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=1122d0558bf6a2d160d96efcc6366a6e95fa8252 commit 1122d0558bf6a2d160d96efcc6366a6e95fa8252 Author: Matthew Thode <prometheanfire@gentoo.org> AuthorDate: 2021-04-27 02:57:38 +0000 Commit: Matthew Thode <prometheanfire@gentoo.org> CommitDate: 2021-04-27 02:57:53 +0000 media-sound/mangler: more c++11 fixes Closes: https://bugs.gentoo.org/784401 Package-Manager: Portage-3.0.18, Repoman-3.0.2 RepoMan-Options: --force Signed-off-by: Matthew Thode <prometheanfire@gentoo.org> .../mangler/files/fix_ftbfs_narrowing_conversion.patch | 18 ++++++++++++++++++ ...mangler-1.2.5-r1.ebuild => mangler-1.2.5-r2.ebuild} | 5 ++++- 2 files changed, 22 insertions(+), 1 deletion(-)