Check in prebuilt flex-2.5.39

Bug: 14446414
Change-Id: I2c2497ee06ac082a6330fcc230579a97f4078037
diff --git a/darwin-x86/flex/PREBUILT b/darwin-x86/flex/PREBUILT
index 9a98850..752e6a1 100644
--- a/darwin-x86/flex/PREBUILT
+++ b/darwin-x86/flex/PREBUILT
@@ -1,4 +1,4 @@
 The objects in this prebuilt directory can be rebuilt
 using the source archive hosted at
 
-http://prdownloads.sourceforge.net/flex/flex-2.5.4a.tar.gz?download
+http://sourceforge.net/projects/flex/files/