Looks like bug #448736 was fixed in 6.3.1, at least it doesn't fail to compile anymore. Can we get it stable?
[QA] The mobile-phone herd has been dissolved to maintainer-needed due to absence. This package has no maintainer so this bug may go unnoticed for a long time. Gentoo has a dedicated team[1] for assisting users in maintaining orphaned packages. If you are interested in maintaining this package, please contact proxy-maint@gentoo.org. [1]: https://wiki.gentoo.org/index.php?title=Project:Proxy_Maintainers
amd64 done
x86 stable, closing