[CMake] Generate cmake target that other libraries can use

... to express their dependency on this library and retrieve any
configuration information such as the include directory, binary
to link to (if any), transitive dependencies, necessary compiler
options or the required c++ standards level.

CMakeLists.txt

@@ -0,0 +1,7 @@
+cmake_minimum_required(VERSION 3.8)
+project(boost-config LANGUAGES CXX)
+
+add_library(boost_config INTERFACE)
+add_library(Boost::config ALIAS boost_config)
+
+target_include_directories(boost_config INTERFACE include)