Windows GDK Support (#5830)

* Added GDK

* Simplfied checks in SDL_config_wingdk.h

* Added testgdk sample

* Added GDK readme

* Fixed error in merge of SDL_windows.h

* Additional GDK fixes

* OpenWatcom should not export _SDL_GDKGetTaskQueue

* Formatting fixes

* Moved initialization code into SDL_GDKRunApp

src/joystick/SDL_joystick.c

@@ -37,7 +37,7 @@
 /* This is included in only one place because it has a large static list of controllers */
 #include "controller_type.h"
 
-#ifdef __WIN32__
+#if defined(__WIN32__) || defined(__WINGDK__)
 /* Needed for checking for input remapping programs */
 #include "../core/windows/SDL_windows.h"
 
@@ -2362,7 +2362,7 @@ static SDL_JoystickType SDL_GetJoystickGUIDType(SDL_JoystickGUID guid)
 
 static SDL_bool SDL_IsPS4RemapperRunning(void)
 {
-#ifdef __WIN32__
+#if defined(__WIN32__) || defined(__WINGDK__)
     const char *mapper_processes[] = {
         "DS4Windows.exe",
         "InputMapper.exe",