64-bit/TEMP: fix crazy wx issue in GameDatabase

Wasn't compiling because of C++ and wx shenanigans. See #308 for an overview.

Unsure if this solution is the good one.
osx: zlib is at same location as Linux
osx: TLS vars (__thread) are supported

Tested on OSX 10.9.4, Xcode 5.1 clang.

Issue #304