Move fclose_deleter and null_deleter to their own namespaces to block ADL.

This prevents bringing namespace boost into ADL when the deleters are used
in template parameters, e.g. in std::unique_ptr.

test/Jamfile.v2

@@ -187,7 +187,12 @@ compile-fail scoped_enum_compile_fail_conv_to_int.cpp
 
 run underlying_type.cpp ;
 
+compile-fail null_deleter_compile_fail_adl.cpp
+  : $(warnings-as-errors-off) ;
+
 run fclose_deleter_test.cpp : : : <target-os>windows:<define>_CRT_SECURE_NO_WARNINGS <target-os>windows:<define>_CRT_SECURE_NO_DEPRECATE ;
+compile-fail fclose_deleter_compile_fail_adl.cpp
+  : <target-os>windows:<define>_CRT_SECURE_NO_WARNINGS <target-os>windows:<define>_CRT_SECURE_NO_DEPRECATE $(warnings-as-errors-off) ;
 
 run functor_test.cpp ;
 

test/fclose_deleter_compile_fail_adl.cpp

@@ -0,0 +1,30 @@
+/*
+ *             Copyright Andrey Semashev 2024.
+ * Distributed under the Boost Software License, Version 1.0.
+ *    (See accompanying file LICENSE_1_0.txt or copy at
+ *          http://www.boost.org/LICENSE_1_0.txt)
+ */
+/*!
+ * \file   fclose_deleter_compile_fail_adl.cpp
+ * \author Andrey Semashev
+ * \date   02.02.2024
+ *
+ * This file tests that \c boost::fclose_deleter doesn't bring namespace
+ * boost into ADL.
+ */
+
+#include <boost/core/fclose_deleter.hpp>
+
+namespace boost {
+
+void check_adl(fclose_deleter const&)
+{
+}
+
+} // namespace boost
+
+int main()
+{
+    // Must not find boost::check_adl
+    check_adl(boost::fclose_deleter());
+}

test/null_deleter_compile_fail_adl.cpp

@@ -0,0 +1,30 @@
+/*
+ *             Copyright Andrey Semashev 2024.
+ * Distributed under the Boost Software License, Version 1.0.
+ *    (See accompanying file LICENSE_1_0.txt or copy at
+ *          http://www.boost.org/LICENSE_1_0.txt)
+ */
+/*!
+ * \file   fclose_deleter_compile_fail_adl.cpp
+ * \author Andrey Semashev
+ * \date   02.02.2024
+ *
+ * This file tests that \c boost::null_deleter doesn't bring namespace
+ * boost into ADL.
+ */
+
+#include <boost/core/null_deleter.hpp>
+
+namespace boost {
+
+void check_adl(null_deleter const&)
+{
+}
+
+} // namespace boost
+
+int main()
+{
+    // Must not find boost::check_adl
+    check_adl(boost::null_deleter());
+}