Linux: Add hint for disabling deadzones

include/SDL_hints.h

@@ -696,6 +696,18 @@ extern "C" {
   */
 #define SDL_HINT_JOYSTICK_RAWINPUT "SDL_JOYSTICK_RAWINPUT"
 
+ /**
+  *  \brief  A variable controlling whether Linux joysticks adhere their HID-defined deadzones or return unfiltered values.
+  *      This is useful for Wine which implements its own deadzone handler if requested by games, also it enables xinput
+  *      games to receive unfiltered values as required from the API.
+  *
+  *  This variable can be set to the following values:
+  *    "0"       - Linux deadzones are not used by SDL
+  *    "1"       - Linux deadzones are used by SDL (the default)
+  *
+  */
+#define SDL_HINT_LINUX_JOYSTICK_DEADZONES "SDL_LINUX_JOYSTICK_DEADZONES"
+
 /**
  *  \brief If set to "0" then never set the top most bit on a SDL Window, even if the video mode expects it.
  *      This is a debugging aid for developers and not expected to be used by end users. The default is "1"

src/joystick/linux/SDL_sysjoystick.c

@@ -38,6 +38,7 @@
 #include <linux/joystick.h>
 
 #include "SDL_assert.h"
+#include "SDL_hints.h"
 #include "SDL_joystick.h"
 #include "SDL_endian.h"
 #include "SDL_timer.h"
@@ -706,6 +707,7 @@ ConfigJoystick(SDL_Joystick * joystick, int fd)
             }
             if (test_bit(i, absbit)) {
                 struct input_absinfo absinfo;
+                SDL_bool hint_used = SDL_GetHintBoolean(SDL_HINT_LINUX_JOYSTICK_DEADZONES, SDL_TRUE);
 
                 if (ioctl(fd, EVIOCGABS(i), &absinfo) < 0) {
                     continue;
@@ -721,7 +723,7 @@ ConfigJoystick(SDL_Joystick * joystick, int fd)
                 if (absinfo.minimum == absinfo.maximum) {
                     joystick->hwdata->abs_correct[i].used = 0;
                 } else {
-                    joystick->hwdata->abs_correct[i].used = 1;
+                    joystick->hwdata->abs_correct[i].used = hint_used;
                     joystick->hwdata->abs_correct[i].coef[0] =
                         (absinfo.maximum + absinfo.minimum) - 2 * absinfo.flat;
                     joystick->hwdata->abs_correct[i].coef[1] =