Override the previous definition from IR object

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.
6 files changed