No need to check version if symbol is unreferenced and undefined.
bfd/
PR ld/20306
* elflink.c (elf_link_check_versioned_symbol): Return false
for unreferenced undefined symbol.
ld/testsuite/
* testsuite/ld-gc/gc.exp: Run pr20306 test.
* ld-gc/pr20306.c: New file.
* ld-gc/pr20306.d: Likewise.
