Hi, I'm awilfox from IRC; it appears the ki18n patch (third link) and ksolid patch (first link) are already applied.
The second link is for KIO's Proxy Autoconfiguration service. It doesn't compile on musl because either ```_BSD_SOURCE``` or ```_GNU_SOURCE``` needs to be defined first. I suggested in the [KDE bug](https://bugs.kde.org/show_bug.cgi?id=365925) to modify ```src/kpac/ConfigureChecks.cmake```, but they haven't responded yet. In the meantime, an easy fix is [this patch](https://code.foxkit.us/adelie/patches/raw/master/kde-frameworks/kio/kio-5.21.0-bsd_source-definition.patch) I wrote that simply adds ```#define _BSD_SOURCE``` to the top of ```src/kpac/kpac_dhcp_helper.c```.
Otherwise, these packages should work on x86_64-musl as far as I can see.
Thank you @Duncaen and @awilfox!
I can confirm, that I've already applied @awilfox's patch to ki18n, and ksolid patch already applied by someone.
Unfortunately i can't test kio patch at this moment, because something broken in qt5 crossbuilding with gcc 6.2, or it's just for me, but I'll try again later