Move stuff from prebuilt to prebuilts/tools

Change-Id: If9a286060abf7bf833a3c54965615826c483c1f3
diff --git a/darwin-x86/jetcreator/PREBUILT b/darwin-x86/jetcreator/PREBUILT
new file mode 100644
index 0000000..b788d6f
--- /dev/null
+++ b/darwin-x86/jetcreator/PREBUILT
@@ -0,0 +1,2 @@
+The object in this prebuilt directory can be rebuilt
+using the source located in external/sonivox/arm-wt-22k/jetcreator_lib_src/darwin-x86/