newly cloned section.
* ld-x86-64/split-by-file.rd: New test.
* ld-x86-64/split-by-file1.s: New test source code.
* ld-x86-64/split-by-file2.s: New test source code.
* ld-x86-64/x86-64.exp: Run the new test.
* readelf.c (process_section_headers): Mention meaning of 'l'
section flag for x86-64 targets.