Require 'thread' for builder mutex

drbrain · drbrain · commit a2155155e158 · 2013-09-09T16:22:44.000-07:00
This was missed when 05e9e55 was cherry-picked
diff --git a/lib/rubygems/ext/builder.rb b/lib/rubygems/ext/builder.rb
@@ -4,6 +4,8 @@
 # See LICENSE.txt for permissions.
 #++
 
+require 'thread'
+
 class Gem::Ext::Builder
 
   ##
