I don't think there is a **default standard library** for a compiler. For example, for clang, clang will find the libstdc++ on linux but libc++ on macos. It is actually highly platform dependent. The compiler just hardcode these things
in the driver.
That's only true in the abstract.
In practice the compiler, for the user invoking it, has a default standard library defined at build time.
When you invoke CMake without specifying anything, it will just accept the compiler it finds in the PATH, and it will just trust that it has a baked in standard library when you invoke it.
So, in that scenario, what are the steps that CMake would do to discover the path to the metadata file?
Daniel