[libc++] [test] Check for another kind of modulemap typo in lint_modulemap.sh.py.

Verify that the name of the private submodule matches the name of the detail header.

Differential Revision: https://reviews.llvm.org/D117438

NOKEYCHECK=True
GitOrigin-RevId: e93f98f09c86b909d0ba76196cce57399bf23d6f
diff --git a/include/module.modulemap b/include/module.modulemap
index 33e0ecf..e5a92e9 100644
--- a/include/module.modulemap
+++ b/include/module.modulemap
@@ -989,7 +989,7 @@
   module __function_like     { private header "__function_like.h"   export * }
   module __hash_table        {         header "__hash_table"        export * }
   module __locale            { private header "__locale"            export * }
-  module __mbstate           { private header "__mbstate_t.h"       export * }
+  module __mbstate_t         { private header "__mbstate_t.h"       export * }
   module __mutex_base        { private header "__mutex_base"        export * }
   module __node_handle       { private header "__node_handle"       export * }
   module __nullptr           {         header "__nullptr"           export * }