In libFLAC 1.2.1:
The Visual Studio projects are horribly out of date, and they don't include x64 configurations.
Adding them myself, x64 fails to compile due to bitreader.c including x86 assembly blocks with no macros to disable this path.
1.2.1 released in 2007, no maintenance at all in 5 years? Come on, FLAC is a really popular library! That's a pretty poor effort.