Allow older versions of jpeglib without a version number we can report.
#include "system-private.h"
#ifdef HAVE_LIBJPEG
# include <jpeglib.h>
+# ifndef JPEG_LIB_VERSION_MAJOR // Added in JPEGLIB 9
+# define JPEG_LIB_VERSION_MAJOR 8
+# define JPEG_LIB_VERSION_MINOR 0
+# endif // !JPEG_LIB_VERSION_MAJOR
#endif // HAVE_LIBJPEG
#ifdef HAVE_LIBPNG
# include <png.h>
