* autodoc: init support for usingnamespace decls * autodoc: don't build autodoc when building zig2.c * autodoc: usingnamespace decls support in frontend (#15203) * autodoc: init support for usingnamespace decls * autodoc: usingnamespace decls support in frontend --------- Co-authored-by: Krzysztof Wolicki <46651553+der-teufel-programming@users.noreply.github.com>