Move stuff from prebuilt/ to prebuilts/misc

Change-Id: Ia54ee1be4b81a1ca73e93355a36bab23b7012665
diff --git a/darwin-x86/flex/PREBUILT b/darwin-x86/flex/PREBUILT
new file mode 100644
index 0000000..9a98850
--- /dev/null
+++ b/darwin-x86/flex/PREBUILT
@@ -0,0 +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