* ld.texinfo (Expression Section): Describe treatment of numbers

	* ld.texinfo (Expression Section): Describe treatment of numbers
	and absolute symbols.
	* ldemul.c (after_open_default): Look up __ld_compatibility.
	* ldexp.c (fold_name): Convert absolute symbols to numbers when
	inside output section definitions, or when __ld_compatibility >= 221.
	(exp_fold_tree_1): Convert numbers to absolute when not in output
	section definition and __ld_compatibility < 221.  Don't always
	convert values outside an output section definition to absolute.
	* ldexp.h (uses_defined): Comment.
	* ldlang.c (ld_compatibility): New variable.
	* ldlang.h (ld_compatibility): Declare.
	* emultempl/aix.em, * emultempl/armcoff.em, * emultempl/beos.em,
	* emultempl/elf32.em, * emultempl/genelf.em, * emultempl/lnk960.em,
	* emultempl/m68kcoff.em, * emultempl/mmo.em, * emultempl/pe.em,
	* emultempl/pep.em, * emultempl/sunos.em, * emultempl/z80.em: Call
	after_open_default from after_open function.