Add convenience macro for native program entrypoint

sdk/src/native_program.rs

@@ -6,3 +6,15 @@ pub const ENTRYPOINT: &str = "process";
 // Native program ENTRYPOINT prototype
 pub type Entrypoint =
     unsafe extern "C" fn(keyed_accounts: &mut [KeyedAccount], data: &[u8]) -> bool;
+
+// Convenience macro to define the native program entrypoint.  Supply a fn to this macro that
+// conforms to the `Entrypoint` type signature.
+#[macro_export]
+macro_rules! solana_entrypoint(
+    ($entrypoint:ident) => (
+        #[no_mangle]
+        pub extern "C" fn process(keyed_accounts: &mut [KeyedAccount], data: &[u8]) -> bool {
+            return $entrypoint(keyed_accounts, data);
+        }
+    )
+);