Ed, In commit r232377 (aka 2be75957b80b640c0aac4356ab861edd0c2f1b9d in the git repo) you added a new header to the include/precompiled directory. That wasn't mentioned in the ChangeLog, wasn't in the patch posted to https://gcc.gnu.org/legacy-ml/libstdc++/2016-01/msg00016.html and wasn't added to include/Makefile.am, which means it never gets precompiled, and never gets installed.
I don't think it was meant to be committed, so I think we should remove it. Any objection? We *could* add it to the build so it gets installed ... but meh.
commit e26e9e928d5562387bc48fc4735a000eceb8d171 Author: Jonathan Wakely <jwak...@redhat.com> Date: Fri Oct 16 00:19:17 2020 libstdc++: Remove unused header This header was not part of the patch submitted and reviewed, and was not added to include/Makefile.am so never gets installed anyway. It appears to have been committed by mistake, so let's remove it. libstdc++-v3/ChangeLog: * include/precompiled/expc++.h: Removed. diff --git a/libstdc++-v3/include/precompiled/expc++.h b/libstdc++-v3/include/precompiled/expc++.h deleted file mode 100644 index 28b6fe9420b..00000000000 --- a/libstdc++-v3/include/precompiled/expc++.h +++ /dev/null @@ -1,57 +0,0 @@ -// C++ includes used for precompiling extensions -*- C++ -*- - -// Copyright (C) 2006-2020 Free Software Foundation, Inc. -// -// This file is part of the GNU ISO C++ Library. This library is free -// software; you can redistribute it and/or modify it under the -// terms of the GNU General Public License as published by the -// Free Software Foundation; either version 3, or (at your option) -// any later version. - -// This library is distributed in the hope that it will be useful, -// but WITHOUT ANY WARRANTY; without even the implied warranty of -// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the -// GNU General Public License for more details. - -// Under Section 7 of GPL version 3, you are granted additional -// permissions described in the GCC Runtime Library Exception, version -// 3.1, as published by the Free Software Foundation. - -// You should have received a copy of the GNU General Public License and -// a copy of the GCC Runtime Library Exception along with this program; -// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see -// <http://www.gnu.org/licenses/>. - -/** @file expc++.h - * This is an implementation file for a precompiled header. - */ - -#if __cplusplus < 201103L -#include <bits/extc++.h> -#endif - -#if __cplusplus > 201103L -#include <experimental/algorithm> -#include <experimental/any> -#include <experimental/chrono> -#include <experimental/deque> -#include <experimental/filesystem> -#include <experimental/forward_list> -#include <experimental/functional> -#include <experimental/iterator> -#include <experimental/list> -#include <experimental/map> -#include <experimental/memory> -#include <experimental/numeric> -#include <experimental/optional> -#include <experimental/ratio> -#include <experimental/set> -#include <experimental/string> -#include <experimental/string_view> -#include <experimental/system_error> -#include <experimental/tuple> -#include <experimental/type_traits> -#include <experimental/unordered_map> -#include <experimental/unordered_set> -#include <experimental/vector> -#endif