For my own code I use "-Wall -Wextra -Werror" + a handful of warnings that are not in this set (like -Wsign-conversion) - and a similar draconian warning set on

For my own code I use "-Wall -Wextra -Werror" + a handful of warnings that are not in this set (like -Wsign-conversion) - and a similar draconian warning set on MSVC, both when building locally during development and on CI. But since my libraries don't ship with build system files those build process decisions are my own and don't "leak" to the users of my libraries (e.g. it wouldn't even enter my mind to dictate a specific build system or build settings on my library users, I know how bad it is to deal with overengineered cmake files of other people). When integrating other libraries I usually also just throw away the 1000+ lines of cmake files they come with and replace them with a few dozen lines of cmake script of my own (I wish that would be an exaggeration or a joke, but it's not - especially when it comes to "professional" C++ libraries coming out of Khronos or Google).