Fix build with Leptonica >=1.83

[quaqo]

From leptonica 1.83 release notes:

• Use stdatomic.h to make cloning string safe. Remove all GetRefcount() and ChangeRefcount() accessors.
• Remove information about fields in many structs from the public interface allheaders.h, instead putting them in internal files pix_internal.h, array_internal.h and ccbord_internal.h.

[quaqo]

Maybe @zdenop is interested in this.

[zdenop]

thanks.

[quaqo]

thanks.

@zdenop I added another commit for configure.ac