ELF: Hide symbols defined in discarded input sections

ELF: Hide symbols defined in discarded input sections

When assigning symbol version, we should hide debug symbols defined in
discarded sections from IR objects so that they can be removed later.

bfd/

	PR ld/23818
	* elflink.c (_bfd_elf_link_assign_sym_version): Hide symbols
	defined in discarded input sections.

ld/

	PR ld/23818
	* testsuite/ld-plugin/lto.exp: Run PR ld/23818 test.
	* testsuite/ld-plugin/pr23818.d: New file.
	* testsuite/ld-plugin/pr23818.t: Likewise.
	* testsuite/ld-plugin/pr23818a.c: Likewise.
	* testsuite/ld-plugin/pr23818b.c: Likewise.