[VM] Fix foreign contracts in VM runtime unhooked

This commit addresses issue diem#781 by including `foreign_contracts` in `vm_runtime/src/lib.rs`.

language/vm/vm_runtime/src/lib.rs

@@ -107,6 +107,9 @@ extern crate rental;
 #[macro_use]
 extern crate mirai_annotations;
 
+#[cfg(feature = "mirai-contracts")]
+pub mod foreign_contracts;
+
 mod block_processor;
 mod counters;
 mod frame;