[libcxx] Fix the function name in exceptions from create_directories

If the nested create_directory call fails, we'd still want to
re-report the errors with the create_directories function name,
which is what the caller called.

This fixes one aspect from MS STL's tests for std::filesystem.

Differential Revision: https://reviews.llvm.org/D102365

NOKEYCHECK=True
GitOrigin-RevId: 68e45962531a25a0fab63eab163a6c9f84c81f1e
diff --git a/src/filesystem/operations.cpp b/src/filesystem/operations.cpp
index 99001a0..5179eea 100644
--- a/src/filesystem/operations.cpp
+++ b/src/filesystem/operations.cpp
@@ -1022,7 +1022,10 @@
     } else if (not is_directory(parent_st))
       return err.report(errc::not_a_directory);
   }
-  return __create_directory(p, ec);
+  bool ret = __create_directory(p, &m_ec);
+  if (m_ec)
+    return err.report(m_ec);
+  return ret;
 }
 
 bool __create_directory(const path& p, error_code* ec) {