Add a Boost-friendly subproject case to CMakeLists

CMakeLists.txt

@@ -1,3 +1,33 @@
+if(NOT CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
+
+# Generated by `boostdep --cmake safe_numerics`
+# Copyright 2020, 2021 Peter Dimov
+# Distributed under the Boost Software License, Version 1.0.
+# https://www.boost.org/LICENSE_1_0.txt
+
+cmake_minimum_required(VERSION 3.8...3.20)
+
+project(boost_safe_numerics VERSION "${BOOST_SUPERPROJECT_VERSION}" LANGUAGES CXX)
+
+add_library(boost_safe_numerics INTERFACE)
+add_library(Boost::safe_numerics ALIAS boost_safe_numerics)
+
+target_include_directories(boost_safe_numerics INTERFACE include)
+
+target_link_libraries(boost_safe_numerics
+  INTERFACE
+    Boost::concept_check
+    Boost::config
+    Boost::core
+    Boost::integer
+    Boost::logic
+    Boost::mp11
+)
+
+target_compile_features(boost_safe_numerics INTERFACE cxx_std_14)
+
+else()
+
 # CMake build control file for safe numerics Library Examples
 
 cmake_minimum_required(VERSION 3.8.6)
@@ -129,3 +159,4 @@ add_subdirectory("include/boost/safe_numerics")
 add_subdirectory("example")
 add_subdirectory("test")
 
+endif()