Fix objdiff-wasm compilation errors

Author: LagoLunatic

objdiff-core/src/arch/mod.rs

@@ -220,7 +220,7 @@ pub trait Arch: Send + Sync + Debug {
         _relocations: &[Relocation],
         _symbols: &[Symbol],
     ) -> Vec<Relocation> {
-        vec![]
+        Vec::new()
     }
 
     fn implcit_addend(

objdiff-core/src/arch/ppc.rs

@@ -1,10 +1,9 @@
 use alloc::{
-    collections::BTreeMap,
+    collections::{BTreeMap, BTreeSet},
     string::{String, ToString},
     vec,
     vec::Vec,
 };
-use std::collections::BTreeSet;
 
 use anyhow::{bail, ensure, Result};
 use cwextab::{decode_extab, ExceptionTableData};