Add CMake Interface Library

[jwillikers]

I am very interested in using your library. I would like to use FetchContent and have access to your library through add_subdirectory. However, your library does not create a convenience target to use with target_link_libraries. While it is little effort for me to add the necessary include directory myself, I would much rather just "link" against your header only library like so:

target_link_libraries(MyTarget PRIVATE Boost::ut)

I have included an import prefix to mirror Boost's component linking behavior.
Defining an interface library through CMake with the appropriate include directories will make this possible.
The changes might look like the following.

add_library(ut INTERFACE)
add_library(Boost::ut ALIAS ut)
target_include_directories(ut INTERFACE $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>)

This code also paves the way for the interface target to be exported and included with find_package.

[krzysztof-jusiak]

Thanks, @athrun22, it should be fixed now, let me know if it works for you 🤔

[jwillikers]

@krzysztof-jusiak, thanks! The interface library works perfectly 😃😃😃