Implement one-definition-rule (ODR) feature.

When compiling multiple RS files, we say two RS files A and B break ODR
iff:

1. They have at least one common struct named [S] and [S] will be reflected
to ScriptField_[S].java, and
2. [S] defined in A is not *exactly the same* (number of fields, field
type and field name) as the one defined in B.

This CL detects such error.
diff --git a/Android.mk b/Android.mk
index 05066e5..0a8dc14 100644
--- a/Android.mk
+++ b/Android.mk
@@ -202,6 +202,7 @@
 	slang_rs_context.cpp	\
 	slang_rs_pragma_handler.cpp	\
 	slang_rs_backend.cpp	\
+	slang_rs_exportable.cpp	\
 	slang_rs_export_type.cpp	\
 	slang_rs_export_element.cpp	\
 	slang_rs_export_var.cpp	\