ld: Set non_ir_ref_regular for --undefined SYMBOL

Set non_ir_ref_regular to TRUE for symbols forced into the output file
so that they won't be removed by garbage collection with LTO.

	PR ld/23309
	* ldlang.c (insert_undefined): Set non_ir_ref_regular to TRUE.
	* plugin.c (is_visible_from_outside): Don't scan entry_symbol.
	* testsuite/ld-plugin/pr23309.c: New file.
	* testsuite/ld-plugin/pr23309.d: Likewise.
6 files changed