I'm pretty sure that the GoldSource engine is and always has been 32-bit, but I've noticed that the Linux/dedicated server builds have a few _amd64.so files (and equivalent _i686.so files).
I'm guessing that the _amd64.so files are just unused but does anyone know why they're there or when they started shipping? I'm pretty sure they've been there since before Counter-Strike had a Linux port anyway.