PR ld/20276: Set non_ir_ref on common symbol

PR ld/20276: Set non_ir_ref on common symbol

Also, don't check alignment on symbol from plugin dummy input.

bfd/
	PR ld/20276
	* elflink.c (elf_link_add_object_symbols): Don't check alignment
	on symbol from plugin dummy input.
ld/
	PR ld/20276
	* plugin.c (plugin_notice): Set non_ir_ref on common symbols.
	* testsuite/ld-plugin/lto.exp (lto_link_tests): Add test for
	PR ld/20276.
	(lto_run_tests): Likewise.
	* testsuite/ld-plugin/pass.out: New file.
	* testsuite/ld-plugin/pr20276a.c: Likewise.
	* testsuite/ld-plugin/pr20276b.c: Likewise.