[libc++] Remove experimental/algorithm

[philnik]

Summary

The only thing left in experimental/algorithm is std::search() with a Searcher and that has been implemented in d835e59211883, which was part of LLVM7.

[• Quuxplusone]

Seems plausible to me, but there should be a ton of libcxx/test/ diffs here. I don't think buildkite ran on this... but I can't figure out why not.

Please git grep experimental/algorithm ../libcxx and fix what you find.

[philnik]

• Remove experimental/algorithm from tests

[Mordante]

In D119585#3315670, @Quuxplusone wrote:

Please git grep experimental/algorithm ../libcxx and fix what you find.

Nice catch @Quuxplusone, it seems our CI coverage isn't good enough. @philnik do want to look at why the CI didn't catch this?

[philnik]

Rebased

[philnik]

• Disable searcher tests in c++14

[• Quuxplusone]

This is related to D119198: std::experimental::search works hand-in-hand with std::experimental::boyer_moore_searcher and company. We can't remove std::experimental::boyer_moore_searcher because we have not yet implemented C++17 std::boyer_moore_searcher
https://en.cppreference.com/w/cpp/utility/functional/boyer_moore_searcher
In this PR, @philnik observes that we could remove std::experimental::search, and just tell people to use std::experimental::boyer_moore_searcher with std::search instead.
In D119198, @jloser observed that we could remove std::experimental::default_searcher, and just tell people to use std::default_searcher with std::experimental::search instead.
But we can't remove all of the experimental searcher stuff in one fell swoop yet, because we haven't implemented the C++17 equivalents.

D119585 seems to me slightly more acceptable than D119198... but guys, we should just implement the C++17 searchers already! @philnik, do you want to take that on?

libcxx/include/CMakeLists.txt

set(files
   cwchar
   cwctype
   deque
   errno.h
   exception
   execution
   experimental/__config
   experimental/__memory
-  experimental/algorithm
   experimental/coroutine
   experimental/deque
   experimental/filesystem
   experimental/forward_list
   experimental/functional
   experimental/iterator
   experimental/list
   experimental/map

libcxx/include/experimental/algorithm

-// -*- C++ -*-
-//===----------------------------------------------------------------------===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-#ifndef _LIBCPP_EXPERIMENTAL_ALGORITHM
-#define _LIBCPP_EXPERIMENTAL_ALGORITHM
-
-/*
-   experimental/algorithm synopsis
-
-#include <algorithm>
-
-namespace std {
-namespace experimental {
-inline namespace fundamentals_v1 {
-
-template <class ForwardIterator, class Searcher>
-ForwardIterator search(ForwardIterator first, ForwardIterator last,
-                       const Searcher &searcher);
-
-// sample removed because it's now part of C++17
-
-} // namespace fundamentals_v1
-} // namespace experimental
-} // namespace std
-
-*/
-
-#include <__debug>
-#include <algorithm>
-#include <experimental/__config>
-#include <type_traits>
-
-#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
-#  pragma GCC system_header
-#endif
-
-_LIBCPP_BEGIN_NAMESPACE_LFTS
-
-template <class _ForwardIterator, class _Searcher>
-_LIBCPP_INLINE_VISIBILITY
-_ForwardIterator search(_ForwardIterator __f, _ForwardIterator __l, const _Searcher &__s)
-{ return __s(__f, __l).first; }
-
-_LIBCPP_END_NAMESPACE_LFTS
-
-#endif /* _LIBCPP_EXPERIMENTAL_ALGORITHM */

libcxx/include/module.modulemap

module std [system] {
   module __threading_support {         header "__threading_support" export * }
   module __tree              {         header "__tree"              export * }
   module __tuple             { private header "__tuple"             export * }
   module __undef_macros      {         header "__undef_macros"      export * }
 
   module experimental {
     requires cplusplus11
 
-    module algorithm {
-      header "experimental/algorithm"
-      export *
-    }
      module coroutine {
       requires coroutines
       header "experimental/coroutine"
       export *
     }
     module deque {
       header "experimental/deque"
       export *