The server codebase work required to reintroduce XP support, assuming that it is only for dev work and has no real performance requirements, includes at least the following:

Provide a template specialization of AtomicWord<LONGLONG> and AtomicWord<ULONGLONG> for Windows XP only. That specialization should use a single global mutex to synchronize all access to AtomicWord<LONGLONG> and AtomicWord<ULONGLONG> instances, rather than using the unavailable atomic intrinsics.

Other non-XP features may also need to be supported.