I've played some catchup with the Win32 library today, and HEAD currently builds with 7.4 through 7.8 (32- and 64-bit) and contains some additional bugfixes. Unless some last minute changes come in, this is more or less what we should ship with GHC 7.8.1 final. Let me know when you're ready to roll a new 7.8.1 RC, and I can tag and upload Win32 2.3.0.2 to Hackage.

B.