Added workaround to fileutils for make btest without rbconfig.

  Followed up r63430.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63434 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

Author: hsbt

lib/fileutils.rb

@@ -548,7 +548,11 @@ def mv(src, dest, force: nil, noop: nil, verbose: nil, secure: nil)
   module_function :move
 
   def rename_cannot_overwrite_file?   #:nodoc:
-    /emx/ =~ RbConfig::CONFIG['host_os']
+    if defined?(RbConfig)
+      /emx/ =~ RbConfig::CONFIG['host_os']
+    else
+      /emx/ =~ RUBY_PLATFORM
+    end
   end
   private_module_function :rename_cannot_overwrite_file?
 
@@ -1153,7 +1157,11 @@ module StreamUtils_
     private
 
     def fu_windows?
-      /mswin|mingw|bccwin|emx/ =~ RbConfig::CONFIG['host_os']
+      if defined?(RbConfig)
+        /mswin|mingw|bccwin|emx/ =~ RbConfig::CONFIG['host_os']
+      else
+        /mswin|mingw|bccwin|emx/ =~ RUBY_PLATFORM
+      end
     end
 
     def fu_copy_stream0(src, dest, blksize = nil)   #:nodoc: