Rename native_program.rs to instruction_processor_utils.rs

Prefer the term "instruction processor" over "program". Reserve
the term "native" for the loader and shared object it loads.
Compiling an instruction processor to BPF shouldn't imply changing
to a non-native entrypoint.

sdk/src/instruction_processor_utils.rs

@@ -0,0 +1,31 @@
+use crate::account::KeyedAccount;
+use crate::instruction::InstructionError;
+use crate::pubkey::Pubkey;
+
+// All native programs export a symbol named process()
+pub const ENTRYPOINT: &str = "process";
+
+// Native program ENTRYPOINT prototype
+pub type Entrypoint = unsafe extern "C" fn(
+    program_id: &Pubkey,
+    keyed_accounts: &mut [KeyedAccount],
+    data: &[u8],
+    tick_height: u64,
+) -> Result<(), InstructionError>;
+
+// 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(
+            program_id: &solana_sdk::pubkey::Pubkey,
+            keyed_accounts: &mut [solana_sdk::account::KeyedAccount],
+            data: &[u8],
+            tick_height: u64
+        ) -> Result<(), solana_sdk::instruction::InstructionError> {
+            $entrypoint(program_id, keyed_accounts, data, tick_height)
+        }
+    )
+);