[AE] Windows: Fix audio device enumeration

cherry-picked from https://github.com/plexinc/plex-home-theater-public/commit/2282ea123
Use XbmcThreads::SystemClockMillis() instead of CTimeUtils::GetTimeMS()

cherry-picked from https://github.com/plexinc/plex-home-theater-public/commit/6916ac9e4
Make sure we set up the environment for SSA+fontconfig

cherry-picked from https://github.com/plexinc/plex-home-theater-public/commit/92b267a27
Don't include git_rev.h/git_revision.h in system.h (leads to excessive recompiles)

eventually needs a little Xcode love

based on https://github.com/plexinc/plex-home-theater-public/commit/b7754ff9a
Make sure that m_dll is NULL before we unload the DLL

cherry-picked from https://github.com/plexinc/plex-home-theater-public/commit/418f5dc4a