After some tests, I saw that some packages will take up an unreasonable large amount of time to build. As those are typically not C packages, I decided to filter the list first. I build all packages with a non-sensincal -Wfoobar in CFLAGS and a timeout of one minute. The failing packages (not counting timeouts) give me all (more or less) packages that use C and correctly use the supplied flags: This gave me 12035 packages to work with. (32%).