Add BPF program entrypoint return type (#8111)

programs/bpf/rust/external_spend/src/lib.rs

@@ -2,7 +2,7 @@
 
 extern crate solana_sdk;
 use solana_sdk::{
-    account_info::AccountInfo, entrypoint, program_error::ProgramError, pubkey::Pubkey,
+    account_info::AccountInfo, entrypoint, entrypoint::ProgramResult, pubkey::Pubkey,
 };
 
 entrypoint!(process_instruction);
@@ -10,7 +10,7 @@ fn process_instruction(
     _program_id: &Pubkey,
     accounts: &[AccountInfo],
     _instruction_data: &[u8],
-) -> Result<(), ProgramError> {
+) -> ProgramResult {
     // account 0 is the mint and not owned by this program, any debit of its lamports
     // should result in a failed program execution.  Test to ensure that this debit
     // is seen by the runtime and fails as expected