Pkg-config files generated by CMake do not include the WSL stubs

[SomeoneSerge]

Pkg-config files generated by CMake do not include the stubs: https://github.com/microsoft/DirectX-Headers/blob/7fc7184d25f76f0797438d404733a76251396c83/CMakeLists.txt#L96

To contrast, cflags generated by meson include .../wsl/stubs: Cflags: -I${includedir} -I${includedir} -I${includedir}/wsl/stubs -I${includedir}/directx.

Note that cmake rules do include a conditional target_link_libraries and the generated directx-headers-config.cmake is in fact correct. If only the pkg-config was somehow derived from get_target_property(... DirectX-Headers INTERFACE_INCLUDE_DIRECTORIES) (non-trivial because of generator expressions) the output would've been correct.