https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102664
--- Comment #22 from Jonathan Wakely <redi at gcc dot gnu.org> --- \? is not allowed in a POSIX BRE, and unsupported by Solaris and BSD. The capture group with \( and \) is not supported by /usr/bin/sed on Solaris, but is supported by /usr/xpg4/bin but I guess we can just require users to have their PATH in order.
