stop using g_jit outside of JitInterface

Replace g_jit in x86-64 ASM routines code by m_jit member reference

Source/Core/Core/PowerPC/JitInterface.h

@@ -11,6 +11,7 @@
 
 class CPUCoreBase;
 class PointerWrap;
+class JitBase;
 
 namespace PowerPC
 {
@@ -65,5 +66,8 @@ void InvalidateICache(u32 address, u32 size, bool forced);
 
 void CompileExceptionCheck(ExceptionType type);
 
+/// used for the page fault unit test, don't use outside of tests!
+void SetJit(JitBase* jit);
+
 void Shutdown();
 }