[libc++][NFC] Format expression-equivalent wrappers consistently

Differential Revision: https://reviews.llvm.org/D108144

NOKEYCHECK=True
GitOrigin-RevId: b28cb53eac70b5044b5bd0fef77530fcc6b29fb0
diff --git a/include/variant b/include/variant
index 700e6f3..b0ea73d 100644
--- a/include/variant
+++ b/include/variant
@@ -1718,11 +1718,10 @@
 
 template <class... _Types>
 inline _LIBCPP_INLINE_VISIBILITY
-auto swap(variant<_Types...>& __lhs,
-          variant<_Types...>& __rhs) noexcept(noexcept(__lhs.swap(__rhs)))
-    -> decltype(__lhs.swap(__rhs)) {
-  __lhs.swap(__rhs);
-}
+auto swap(variant<_Types...>& __lhs, variant<_Types...>& __rhs)
+  noexcept(noexcept(__lhs.swap(__rhs)))
+  -> decltype(      __lhs.swap(__rhs))
+  { return          __lhs.swap(__rhs); }
 
 template <class... _Types>
 struct _LIBCPP_TEMPLATE_VIS hash<