This is required in order for us to support deterministic mode by default. If multiple -D or -U options are specified on the command line, the final one takes precedence. GNU ar also uses -U for this. An equivalent change will be applied to ELF Tool Chain's version of ar. PR: 196929 MFC after: 1 month Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D3175