Program feature-flag entrypoint (#11144) (#11152)

(cherry picked from commit 231e2387db)

Co-authored-by: Tyera Eulberg <teulberg@gmail.com>

sdk/src/entrypoint.rs

@@ -35,6 +35,7 @@ pub const SUCCESS: u64 = 0;
 macro_rules! entrypoint {
     ($process_instruction:ident) => {
         /// # Safety
+        #[cfg(feature = "program")]
         #[no_mangle]
         pub unsafe extern "C" fn entrypoint(input: *mut u8) -> u64 {
             let (program_id, accounts, instruction_data) =