This was uncovered by a recent clang change [1]. Different than ISO C, POSIX states that va_list should be exported by wchar.h [2]. Checked on x86_64-linux-gnu and aarch64-linux-gnu. [1] https://reviews.llvm.org/D137268 [2] https://pubs.opengroup.org/onlinepubs/9699919799.2018edition/basedefs/wchar.h.html