gas: Extend .symver directive

gas: Extend .symver directive

Extend .symver directive to update visibility of the original symbol and
assign one original symbol to different versioned symbols:

  .symver foo, foo@VERS_1, local    # Change foo to a local symbol.
  .symver foo, foo@VERS_2, hidden   # Change foo to a hidden symbol.
  .symver foo, foo@@VERS_3, remove  # Remove foo from symbol table.
  .symver foo, bar@V1               # Assign foo to bar@V1 and baz@V2.
  .symver foo, baz@V2

	PR gas/23840
	PR gas/25295
	* NEWS: Mention .symver extension.
	* config/obj-elf.c (obj_elf_find_and_add_versioned_name): New
	function.
	(obj_elf_symver): Call obj_elf_find_and_add_versioned_name to
	add a version name.  Add local, hidden and remove visibility
	support.
	(elf_frob_symbol): Handle the list of version names.  Update the
	original symbol to local, hidden or remove it from the symbol
	table.
	(elf_frob_file_before_adjust): Handle the list of version names.
	* config/obj-elf.h (elf_visibility): New.
	(elf_versioned_name_list): Likewise.
	(elf_obj_sy): Change local to bitfield. Add rename, bad_version
	and visibility.  Change versioned_name pointer to struct
	elf_versioned_name_list.
	* doc/as.texi: Update .symver directive.
	* testsuite/gas/symver/symver.exp: Run all *.d tests.  Add more
	error checking tests.
	* testsuite/gas/symver/symver6.d: New file.
	* testsuite/gas/symver/symver7.d: Likewise.
	* testsuite/gas/symver/symver7.s: Likewise.
	* testsuite/gas/symver/symver8.d: Likewise.
	* testsuite/gas/symver/symver8.s: Likewise.
	* testsuite/gas/symver/symver9.s: Likewise.
	* testsuite/gas/symver/symver9a.d: Likewise.
	* testsuite/gas/symver/symver9b.d: Likewise.
	* testsuite/gas/symver/symver10.s: Likewise.
	* testsuite/gas/symver/symver10a.d: Likewise.
	* testsuite/gas/symver/symver10b.d: Likewise.
	* testsuite/gas/symver/symver11.d: Likewise.
	* testsuite/gas/symver/symver11.s: Likewise.
	* testsuite/gas/symver/symver12.d: Likewise.
	* testsuite/gas/symver/symver12.s: Likewise.
	* testsuite/gas/symver/symver13.d: Likewise.
	* testsuite/gas/symver/symver13.s: Likewise.
	* testsuite/gas/symver/symver14.d: Likewise.
	* testsuite/gas/symver/symver14.l: Likewise.
	* testsuite/gas/symver/symver15.d: Likewise.
	* testsuite/gas/symver/symver15.l: Likewise.
	* testsuite/gas/symver/symver6.l: Removed.
	* testsuite/gas/symver/symver6.s: Updated.