Merge branch 'jk/weather-balloon-require-variadic-macro'

We've carried compatibility codepaths for compilers without variadic macros for quite some time, but the world may be ready for them to be removed. Force compilation failure on exotic platforms where variadic macros are not available to find out who screams in such a way that we can easily revert if it turns out that the world is not yet ready. * jk/weather-balloon-require-variadic-macro: git-compat-util: always enable variadic macros