Sync from upstream.

build/Jamfile.v2

@@ -142,16 +142,10 @@ if ! $(disable-icu)
 exe has_icu : has_icu_test.cpp : $(ICU_OPTS) ;
 explicit has_icu ;
 
-obj is_legacy_03 : is_legacy_03.cpp ;
-explicit is_legacy_03 ;
-
 alias icu_options : : : : [ check-target-builds has_icu : $(ICU_OPTS) : ] ;
 
 SOURCES = 
    posix_api.cpp
-   regex.cpp
-   regex_debug.cpp
-   static_mutex.cpp
    wide_posix_api.cpp
 ;
 

build/is_legacy_03.cpp

@@ -1,16 +0,0 @@
-/*
- *
- * Copyright (c) 2020
- * John Maddock
- *
- * Use, modification and distribution are subject to 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)
- *
- */
-
-#include <boost/regex/config.hpp>
-
-#ifdef BOOST_REGEX_CXX03
-#error "Legacy mode"
-#endif