lint: port missing copy impl diagnostics

Signed-off-by: David Wood <[email protected]>

Author: davidtwco

compiler/rustc_error_messages/locales/en-US/lint.ftl

@@ -326,3 +326,5 @@ lint-builtin-decl-unsafe-method = declaration of an `unsafe` method
 lint-builtin-impl-unsafe-method = implementation of an `unsafe` method
 
 lint-builtin-missing-doc = missing documentation for {$article} {$desc}
+
+lint-builtin-missing-copy-impl = type could implement `Copy`; consider adding `impl Copy`

compiler/rustc_lint/src/builtin.rs

@@ -781,11 +781,7 @@ impl<'tcx> LateLintPass<'tcx> for MissingCopyImplementations {
         .is_ok()
         {
             cx.struct_span_lint(MISSING_COPY_IMPLEMENTATIONS, item.span, |lint| {
-                lint.build(
-                    "type could implement `Copy`; consider adding `impl \
-                          Copy`",
-                )
-                .emit();
+                lint.build(fluent::lint::builtin_missing_copy_impl).emit();
             })
         }
     }