Ensure hard reference for frozen strings

These frozen strings must be hard referenced until the identity
has been tested, or an intervening GC could cause them to get
collected and improperly fail the test. The cross-require global
now points at the string in question and is cleared after the
identity test.

Author: headius

language/fixtures/freeze_magic_comment_across_files.rb

@@ -2,4 +2,5 @@
 
 require_relative 'freeze_magic_comment_required'
 
-p "abc".object_id == $second_literal_id
+p "abc".equal?($second_literal)
+$second_literal = nil

language/fixtures/freeze_magic_comment_across_files_diff_enc.rb

@@ -2,4 +2,5 @@
 
 require_relative 'freeze_magic_comment_required_diff_enc'
 
-p "abc".object_id != $second_literal_id
+p !"abc".equal?($second_literal)
+$second_literal = nil

language/fixtures/freeze_magic_comment_across_files_no_comment.rb

@@ -2,4 +2,5 @@
 
 require_relative 'freeze_magic_comment_required_no_comment'
 
-p "abc".object_id != $second_literal_id
+p !"abc".equal?($second_literal)
+$second_literal = nil

language/fixtures/freeze_magic_comment_one_literal.rb

@@ -1,4 +1,4 @@
 # frozen_string_literal: true
 
-ids = Array.new(2) { "abc".object_id }
-p ids.first == ids.last
+objs = Array.new(2) { "abc" }
+p objs.first.equal?(objs.last)

language/fixtures/freeze_magic_comment_required.rb

@@ -1,3 +1,3 @@
 # frozen_string_literal: true
 
-$second_literal_id = "abc".object_id
+$second_literal = "abc"

language/fixtures/freeze_magic_comment_required_diff_enc.rb

@@ -1,4 +1,4 @@
 # encoding: euc-jp # built-in for old regexp option
 # frozen_string_literal: true
 
-$second_literal_id = "abc".object_id
+$second_literal = "abc"

language/fixtures/freeze_magic_comment_required_no_comment.rb

@@ -1 +1 @@
-$second_literal_id = "abc".object_id
+$second_literal = "abc"