Add support for modular build structure. (#2905)

* Use beast exclusive valgrind feature.

* Make the library modular usable.

* Switch to library requirements instead of source. As source puts extra source in install targets.

* Add Beast root dir for includes. As some tests refer to files relative to that.

* Replace relative docca refs with project based.

* Avoid mtuliple openssl configurations.

* Always declare openssl. If it's empty and duplicate it will be ignored.

* Add missing import-search for cconfig/predef checks.

* Add requires-b2 check to top-level build file.

* Bump B2 require to 5.2

* Update copyright dates.

* Move inter-lib dependencies to a project variable and into the build targets.

* Update build deps.

* Update build deps.

* The http/client/body example uses the source header from json instead of the linked library.

build.jam

@@ -0,0 +1,74 @@
+# Copyright René Ferdinand Rivera Morell 2023-2024
+# 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)
+
+require-b2 5.2 ;
+
+import feature ;
+
+constant boost_dependencies :
+    /boost/asio//boost_asio
+    /boost/assert//boost_assert
+    /boost/bind//boost_bind
+    /boost/config//boost_config
+    /boost/container//boost_container
+    /boost/container_hash//boost_container_hash
+    /boost/core//boost_core
+    /boost/endian//boost_endian
+    /boost/intrusive//boost_intrusive
+    /boost/logic//boost_logic
+    /boost/mp11//boost_mp11
+    /boost/optional//boost_optional
+    /boost/preprocessor//boost_preprocessor
+    /boost/smart_ptr//boost_smart_ptr
+    /boost/static_assert//boost_static_assert
+    /boost/static_string//boost_static_string
+    /boost/system//boost_system
+    /boost/throw_exception//boost_throw_exception
+    /boost/type_index//boost_type_index
+    /boost/type_traits//boost_type_traits
+    /boost/winapi//boost_winapi ;
+
+project /boost/beast
+    : common-requirements
+        <include>include
+    ;
+
+explicit
+    [ alias boost_beast : build//boost_beast ]
+    [ alias boost_beast_asio : build//boost_beast_asio ]
+    [ alias boost_beast_asio_ssl : build//boost_beast_asio_ssl ]
+    [ alias all : boost_beast boost_beast_asio boost_beast_asio_ssl example test ]
+    # Old-style targets. Remove once the rest of Beast changes.
+    [ alias lib-beast : boost_beast ]
+    [ alias lib-asio : boost_beast_asio ]
+    [ alias lib-asio-ssl : boost_beast_asio_ssl ]
+    ;
+
+call-if : boost-library beast
+    : install boost_beast boost_beast_asio boost_beast_asio_ssl
+    ;
+
+feature.feature boost.beast.allow-deprecated : on off : propagated ;
+feature.feature boost.beast.separate-compilation : on off : propagated ;
+feature.feature boost.beast.valgrind : on off : optional propagated ;
+
+variant beast_coverage
+    : debug
+    : <cxxflags>"-msse4.2 --coverage"
+        <linkflags>"--coverage"
+    ;
+
+variant beast_valgrind
+    : release
+    : <boost.beast.valgrind>on
+    ;
+
+variant beast_ubasan
+    : release
+    : <cxxflags>"-msse4.2 -funsigned-char -fno-omit-frame-pointer -fsanitize=address,undefined -fno-sanitize-recover=address,undefined -fsanitize-blacklist=libs/beast/tools/blacklist.supp"
+        <linkflags>"-fsanitize=address,undefined"
+        <define>BOOST_USE_ASAN=1
+    ;
+