[libcxx][functional][modular] splices <functional> into modular headers

Differential Revision: https://reviews.llvm.org/D104942

NOKEYCHECK=True
GitOrigin-RevId: 050b064f15ee56ee0b42c9b957a3dd0f32532394
diff --git a/include/map b/include/map
index 0da590f..513a04d 100644
--- a/include/map
+++ b/include/map
@@ -491,6 +491,7 @@
 
 #include <__config>
 #include <__debug>
+#include <__functional/is_transparent.h>
 #include <__node_handle>
 #include <__tree>
 #include <__utility/forward.h>