Split out Rust BPF no-std stuff (#4968)

programs/bpf/rust/128bit_dep/src/lib.rs

@@ -7,3 +7,14 @@ extern crate solana_sdk_bpf_utils;
 pub fn work(x: u128, y: u128) -> u128 {
     x + y
 }
+
+#[cfg(test)]
+mod test {
+    extern crate std;
+    use super::*;
+
+    #[test]
+    fn test_work() {
+        assert_eq!(3, work(1, 2));
+    }
+}