My impression is that a lot of the fallout was related to checks in configure scripts and equivalent. That kind of code was traditionally written a lot more slo

My impression is that a lot of the fallout was related to checks in configure scripts and equivalent. That kind of code was traditionally written a lot more sloppily and was much less likely to have the "standard" set of warnings or the make-warnings-into-errors flag enabled. So, yes, quite a lot of packages failed to build, but the offending code was typically not code that was run when somebody was actually using the program and not code where bugs were consequential. And of course Fedora's a big collection of software with a pretty long tail -- 10% of packages likely works out to a lot less than 10% of user-executing-a-program hours.