jit64: enable faddsx again

It was disabled because of issue 182, but as this game depeneds on FPRF, it was just 'fixed' because of the fallback to interpreter (which implements FPRF by default).
Also enables FPRF for this game via GameIni, so that the issue is still workaround.

If there are any regressions because of this commit, please try to enable FPRF in GameIni.
[Netplay] Allow a spectator to leave without affecting players.
Document some UGeckoInstruction fields
Fix out-of-tree build on OS X.
Fix TextureEncoder.h
Basic precompiled header support for Linux/OS X.  Shaves 20-30% off full rebuild time on my system.
Fix a filter in the VS project file for JitILCommon-related files.