fix bare imports in `format: 'cjs'` mode (#4050)

src/compiler/compile/create_module.ts

@@ -152,7 +152,12 @@ function cjs(
 
 	const internal_globals = get_internal_globals(globals, helpers);
 
-	const user_requires = imports.map(node => ({
+	const user_requires = imports.map(node => {
+		const init = x`require("${edit_source(node.source.value, sveltePath)}")`;
+		if (node.specifiers.length === 0) {
+			return b`${init};`;
+		}
+		return {
 			type: 'VariableDeclaration',
 			kind: 'const',
 			declarations: [{
@@ -171,9 +176,10 @@ function cjs(
 							kind: 'init'
 						}))
 					},
-			init: x`require("${edit_source(node.source.value, sveltePath)}")`
+				init
 			}]
-	}));
+		};
+	});
 
 	const exports = module_exports.map(x => b`exports.${{ type: 'Identifier', name: x.as }} = ${{ type: 'Identifier', name: x.name }};`);