Add missing extern "C"

Fixes #25

Author: jeroen

src/myrustlib/src/mythreads.rs

@@ -2,7 +2,7 @@ use std::thread;
 use std::time::Duration;
 
 #[no_mangle]
-pub extern fn run_threads() {
+pub extern "C" fn run_threads() {
     thread::spawn(|| {
         for i in 1..10 {
             println!("hi number {} from the spawned thread!", i);

src/myrustlib/src/random.rs

@@ -1,7 +1,7 @@
 use rand::random;
 
 #[no_mangle]
-pub extern fn random_number() -> i32 {
+pub extern "C" fn random_number() -> i32 {
   let tuple = random::<i32>();
   tuple
 }