If it’s not in the AST, it’s not in the translation unit. Try searching the AST dump, maybe you’re looking in the wrong place.
Static analyzer is intended to work more or less correctly regardless of whether the method is present. Like, it doesn’t even have to be libc++ to begin with. But i’d be pretty surprised if the body is there but the static analyzer can’t find it. Most likely something else is going on.
You should be looking for the fully instantiated body, not the original template, because that’s what the static analyzer works with. Clang duplicates the AST for each template instantiation so it should be there if it’s at all available.
I’ve not looked into the libstdc++ code for this, but my guess would be that implicit instantiation of that function’s definition is being suppressed by an explicit instantiation declaration – so the definition of the template might be in the AST, but we’re not allowed to instantiate it even though it was used.