Mark the previous definition from IR object as undefined so that the
generic linker will override it.
bfd/
PR ld/23958
* elflink.c (_bfd_elf_add_default_symbol): Override the previous
definition from IR object.
ld/
PR ld/23958
* testsuite/ld-plugin/lto.exp: Run PR ld/23958 test.
* testsuite/ld-plugin/pr23958.c: New file.
* testsuite/ld-plugin/pr23958.t: Likewise.