fd79b70a87
Versions prior to this didn't compile on OpenBSD due to unconditional use of the non-standard strtod_l() function. The fmt::MemoryWriter API has been removed in the intervening versions, so replace its use with fmt::memory_buffer and fmt::format_to. The library also no longer provides the fmt::fmt ALIAS, so define it in externals/CMakeLists.txt.