Staging packages of 16.12.x for kubuntu failed to build from source on arm64/armhf/ppc64el where char is explicitly unsigned by default, with errors:
<<PKGBUILDDIR>>/ksirk/iris/src/xmpp/base64/base64.cpp:65:2: error: narrowing conversion of ‘-1’ from ‘int’ to ‘char’ inside { } [-Wnarrowing]
Applying a patch with this minor fix allowed successful builds on those architectures.