Use C++ style comments consistently in SDL source code

Implemented using this script:

find . -type f -exec sed -i'' -e 's,/\* *\([^*]*\)\*/ *$,// \1,' -e 's, \+$,,' {} \;
git checkout \
    core/linux/SDL_evdev_kbd_default_keymap.h \
    events/imKStoUCS.* \
    hidapi \
    joystick/controller_type.c \
    joystick/controller_type.h \
    joystick/hidapi/steam/controller_constants.h \
    joystick/hidapi/steam/controller_structs.h \
    joystick/SDL_gamepad_db.h \
    libm \
    render/*/*Shader*.h \
    render/vitagxm/SDL_render_vita_gxm_shaders.h \
    render/metal/SDL_shaders_metal_*.h \
    stdlib/SDL_malloc.c \
    stdlib/SDL_qsort.c \
    stdlib/SDL_strtokr.c \
    test/ \
    video/directx/SDL_d3d12_xbox_cmacros.h \
    video/directx/d3d12.h \
    video/directx/d3d12sdklayers.h \
    video/khronos \
    video/x11/edid-parse.c \
    video/x11/xsettings-client.* \
    video/yuv2rgb
sed -i'' -e 's,/\* *\([^*]*\)\*/ *$,// \1,' -e 's, \+$,,' hidapi/SDL_hidapi.c

src/sensor/coremotion/SDL_coremotionsensor.h

@@ -20,7 +20,7 @@
 */
 #include "SDL_internal.h"
 
-/* The private structure used to keep track of a sensor */
+// The private structure used to keep track of a sensor
 struct sensor_hwdata
 {
     float data[3];

src/sensor/coremotion/SDL_coremotionsensor.m

@@ -22,7 +22,7 @@
 
 #ifdef SDL_SENSOR_COREMOTION
 
-/* This is the system specific header for the SDL sensor API */
+// This is the system specific header for the SDL sensor API
 #include <CoreMotion/CoreMotion.h>
 
 #include "SDL_coremotionsensor.h"
@@ -211,4 +211,4 @@ SDL_SensorDriver SDL_COREMOTION_SensorDriver = {
     SDL_COREMOTION_SensorQuit,
 };
 
-#endif /* SDL_SENSOR_COREMOTION */
+#endif // SDL_SENSOR_COREMOTION