always build an implementation of GCAdapter (either libusb or android)

Source/Core/InputCommon/CMakeLists.txt

@@ -32,13 +32,12 @@ elseif(ANDROID)
 	         ControllerInterface/Android/Android.cpp)
 endif()
 
-if(LIBUSB_FOUND)
-	set(SRCS	${SRCS}	GCAdapter.cpp)
-elseif(ANDROID)
-	set(SRCS	${SRCS}	GCAdapter_Android.cpp)
+if(ANDROID)
+        set(SRCS        ${SRCS} GCAdapter_Android.cpp)
 else()
-	set(SRCS	${SRCS}	GCAdapter_Null.cpp)
-endif(LIBUSB_FOUND)
+        set(SRCS        ${SRCS} GCAdapter.cpp)
+        set(LIBS ${LIBS} ${LIBUSB_LIBRARIES})
+endif()
 
 if(LIBEVDEV_FOUND AND LIBUDEV_FOUND)
 	set(SRCS ${SRCS} ControllerInterface/evdev/evdev.cpp)

Source/Core/InputCommon/GCAdapter_Null.cpp

@@ -1,53 +0,0 @@
-// Copyright 2014 Dolphin Emulator Project
-// Licensed under GPLv2+
-// Refer to the license.txt file included.
-
-#include "InputCommon/GCAdapter.h"
-#include "Common/CommonTypes.h"
-#include "InputCommon/GCPadStatus.h"
-
-namespace GCAdapter
-{
-void Init()
-{
-}
-void ResetRumble()
-{
-}
-void Shutdown()
-{
-}
-void SetAdapterCallback(std::function<void(void)> func)
-{
-}
-void StartScanThread()
-{
-}
-void StopScanThread()
-{
-}
-GCPadStatus Input(int chan)
-{
-  return {};
-}
-void Output(int chan, u8 rumble_command)
-{
-}
-bool IsDetected()
-{
-  return false;
-}
-bool IsDriverDetected()
-{
-  return false;
-}
-bool DeviceConnected(int chan)
-{
-  return false;
-}
-bool UseAdapter()
-{
-  return false;
-}
-
-}  // end of namespace GCAdapter