One problem with this argument is that SQLite is primarily used as a source-level embeddable library. That is, most users of SQLite don't use the official binaries and instead build the source code themselves. So, in practice, the source code, not the official blessed binary, is what matters. When upgrading compilers, developers of apps that embed SQLite don't typically check to ensure that upstream SQLite has tested the new version of their compiler. They just upgrade their compiler and assume that the new version will continue to compile their SQLite source properly. If the new version of the compiler happens to compile programs with undefined behavior differently, then problems can arise.