* ld-elfvers/vers.exp (build_vers_lib): Support linking against
more than one libraries.
Add "vers20a" and "vers20" tests for common symbols.
* ld-elfvers/vers20.c: New.
* ld-elfvers/vers20.dsym: New.
* ld-elfvers/vers20.map: New.
* ld-elfvers/vers20.ver: New.
* ld-elfvers/vers20a.ver: New.
