PR ld/12356

	PR ld/12356
	* ld.texinfo (Miscellaneous Commands): Describe LD_FEATURE.
	(Expression Section): Update.
	* ld.h (ld_config_type): Add sane_expr.
	* ldgram.y (ifile_p1): Add LD_FEATURE.
	* ldlex.l (LD_FEATYRE): New.
	* ldemul.c (after_parse_default): Delete code handling ld_compatibility.
	* ldexp.h (struct ldexp_control): Delete uses_defined.
	* ldexp.c: Remove all uses of uses_defined.
	(fold_name): Test config.sane_expr rather than ld_compatibility.
	(exp_fold_tree_1): Likewise.  Adjust handling of assignments
	during first phase.
	* ldlang.h (ld_compatibility): Delete.
	(lang_ld_feature): Declare.
	* ldlang.c (ld_compatibility): Delete.
	(open_input_bfds): Only handle assignments for --defsym.
	(lang_ld_feature): New function.