Also fix some warnings and potential issues that building the entire EuropaTools codebase under those flags showed.
Later on once we drop the libpixel and stbiw dependencies, we can probably turn on -Werror for release builds.
Instead of using set_target_properties on all tool binaries,
instead we can use target_compile_features([xxx] PUBLIC cxx_std_20).
This properly alienates projects which depend on libeuropa, allowing the src/tools CMakeLists to be trimmed down quite a bit.
Also fixes a build break I accidentally introduced.
