Include GameInput.h as gameinput.h for compatibility with non-MSVC toolchains

CMakeLists.txt

@@ -1882,7 +1882,7 @@ elseif(WINDOWS)
   check_c_source_compiles("
     #include <stdbool.h>
     #define COBJMACROS
-    #include <GameInput.h>
+    #include <gameinput.h>
     int main(int argc, char **argv) { return 0; }" HAVE_GAMEINPUT_H
   )
   check_include_file(dxgi1_6.h HAVE_DXGI1_6_H)

src/joystick/gdk/SDL_gameinputjoystick.c

@@ -27,7 +27,7 @@
 
 #include <stdbool.h>
 #define COBJMACROS
-#include <GameInput.h>
+#include <gameinput.h>
 
 enum
 {

src/video/windows/SDL_windowsgameinput.c

@@ -26,7 +26,7 @@
 
 #include <stdbool.h>
 #define COBJMACROS
-#include <GameInput.h>
+#include <gameinput.h>
 
 #include "../../events/SDL_mouse_c.h"
 #include "../../events/SDL_keyboard_c.h"