Fix b/3427124. Adding the overloadable invokable feature. Reflect that type of invokables to Java.

1. Add __attribute__((overloadable)) support on the rs side for invokables. Requested by the Books team.
2. Add name mangling support and MangleContext.
3. Add the test P_overload.
4. This CL only affects Honeycomb SDK. It doesn't affect Final ROM.
5. This CL should go in at the same time with another CL on external/clang.git (to be done now.)

Change-Id: I9e743894a97626d8c27b0dd9c0a51cef1175d2ab
diff --git a/slang_rs_export_func.cpp b/slang_rs_export_func.cpp
index 95e09f2..f634f0f 100644
--- a/slang_rs_export_func.cpp
+++ b/slang_rs_export_func.cpp
@@ -36,7 +36,7 @@
 
   slangAssert(!Name.empty() && "Function must have a name");
 
-  F = new RSExportFunc(Context, Name);
+  F = new RSExportFunc(Context, Name, FD);
 
   // Initialize mParamPacketType
   if (FD->getNumParams() <= 0) {