added #define _DARWIN_C_SOURCE as in other files to avoid implicit
added #define _DARWIN_C_SOURCE as in other files to avoid implicit

https://github.com/gphoto/libgphoto2/issues/633

gphoto/libgphoto2,gphoto/libgphoto2,gphoto/libgphoto2,gphoto/libgphoto2,gphoto/libgphoto2,gphoto/libgphoto2