Support target_include_directories for BUILD_INTERFACE

[CedricLeon]

Hello, i'm using cJSON as part of a cmake superbuild. So cJSON is built along my project. But i can't just do #include <cJSON.h> since the folder containing this file isn't part of the public linking interface. It would be nice to add something like target_include_directories("${CJSON_LIB}" PUBLIC $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>) after add_library. Would you consider such change? I did an implementation on my own fork.

[KamranAghlami]

I'm dealing with same situation and I think this should've been included into the CMake script as well.