Move all architecture-specific code into modules

No more scattered relocation handling and
feature checks. Everything will go through
the ObjArch trait, which makes it easier
to add new architectures going forward.

objdiff-gui/src/app.rs

@@ -290,7 +290,7 @@ impl App {
                             title: "Error".to_string(),
                             progress_percent: 0.0,
                             progress_items: None,
-                            status: "".to_string(),
+                            status: String::new(),
                             error: Some(err),
                         }));
                     }