Ok, that's what I thought. We should just rename it to X64... that's what we usually do for the common x86/x64 things (see: x64CpuDetect, x64TextureDecoder, JIT64, JITIL64).

@Sonicadvance1 care to make a PR that renames ARMXEmitter -> ARMEmitter and XEmitter -> X64Emitter in the near future? :)