Omit devmajor and devminor for non-special files
* src/create.c (start_header): Leave the devmajor and devminor
fields empty for files that are not character and block special
devices, even when the archive format is pax, ustar or v7.
This avoids generating irrelevant differences which helps with
reproducible builds, and is more compatible with what Solaris 10
tar does.