Remove unused spinlock implementations again

This reverts commit 9f5a48ab3b.

.drone.jsonnet

@@ -226,6 +226,20 @@ local windows_pipeline(name, image, environment, arch = "amd64") =
         "g++-15-multilib",
     ),
 
+    linux_pipeline(
+        "Linux 16.04 Clang 3.5",
+        "cppalliance/droneubuntu1604:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-3.5', CXXSTD: '11' },
+        "clang-3.5",
+    ),
+
+    linux_pipeline(
+        "Linux 16.04 Clang 3.6",
+        "cppalliance/droneubuntu1604:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-3.6', CXXSTD: '11,14' },
+        "clang-3.6",
+    ),
+
     linux_pipeline(
         "Linux 16.04 Clang 3.7",
         "cppalliance/droneubuntu1604:1",

appveyor.yml

@@ -21,6 +21,10 @@ environment:
       TOOLSET: msvc-14.1
       CXXSTD: 14,17
       ADDRMD: 32,64
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
+      TOOLSET: clang-win
+      CXXSTD: 14,17,latest
+      ADDRMD: 64
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
       TOOLSET: msvc-14.2
       CXXSTD: 14

include/boost/smart_ptr/detail/spinlock.hpp

@@ -29,6 +29,16 @@
 //
 
 #include <boost/smart_ptr/detail/deprecated_macros.hpp>
-#include <boost/smart_ptr/detail/spinlock_std_atomic.hpp>
+
+#if defined(__clang__)
+
+// Old Clang versions have trouble with ATOMIC_FLAG_INIT
+# include <boost/smart_ptr/detail/spinlock_gcc_atomic.hpp>
+
+#else
+
+# include <boost/smart_ptr/detail/spinlock_std_atomic.hpp>
+
+#endif
 
 #endif // #ifndef BOOST_SMART_PTR_DETAIL_SPINLOCK_HPP_INCLUDED

include/boost/smart_ptr/detail/spinlock_gcc_atomic.hpp

@@ -0,0 +1,94 @@
+#ifndef BOOST_SMART_PTR_DETAIL_SPINLOCK_GCC_ATOMIC_HPP_INCLUDED
+#define BOOST_SMART_PTR_DETAIL_SPINLOCK_GCC_ATOMIC_HPP_INCLUDED
+
+// MS compatible compilers support #pragma once
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1020)
+# pragma once
+#endif
+
+// Copyright 2008, 2020 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/smart_ptr/detail/yield_k.hpp>
+
+#if defined(BOOST_SP_REPORT_IMPLEMENTATION)
+
+#include <boost/config/pragma_message.hpp>
+BOOST_PRAGMA_MESSAGE("Using __atomic spinlock")
+
+#endif
+
+namespace boost
+{
+
+namespace detail
+{
+
+class spinlock
+{
+public:
+
+    // `bool` alignment is required for Apple PPC32
+    // https://github.com/boostorg/smart_ptr/issues/105
+    // https://github.com/PurpleI2P/i2pd/issues/1726
+    // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107590
+
+    union
+    {
+        unsigned char v_;
+        bool align_;
+    };
+
+public:
+
+    bool try_lock()
+    {
+        return __atomic_test_and_set( &v_, __ATOMIC_ACQUIRE ) == 0;
+    }
+
+    void lock()
+    {
+        for( unsigned k = 0; !try_lock(); ++k )
+        {
+            boost::detail::yield( k );
+        }
+    }
+
+    void unlock()
+    {
+        __atomic_clear( &v_, __ATOMIC_RELEASE );
+    }
+
+public:
+
+    class scoped_lock
+    {
+    private:
+
+        spinlock & sp_;
+
+        scoped_lock( scoped_lock const & );
+        scoped_lock & operator=( scoped_lock const & );
+
+    public:
+
+        explicit scoped_lock( spinlock & sp ): sp_( sp )
+        {
+            sp.lock();
+        }
+
+        ~scoped_lock()
+        {
+            sp_.unlock();
+        }
+    };
+};
+
+} // namespace detail
+} // namespace boost
+
+#define BOOST_DETAIL_SPINLOCK_INIT {{0}}
+
+#endif // #ifndef BOOST_SMART_PTR_DETAIL_SPINLOCK_GCC_ATOMIC_HPP_INCLUDED