Ensure hard reference for frozen strings (#1348)

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"