CMAKE_<LANG>_IMPLICIT_LINK_DIRECTORIES

Compilers typically pass directories containing language runtime libraries and default library search paths when they invoke a linker. These paths are implicit linker search directories for the compiler’s language. CMake automatically detects these directories for each language and reports the results in this variable.

When a library in one of these directories is given by full path to target_link_libraries() CMake will generate the -l<name> form on link lines to ensure the linker searches its implicit directories for the library. Note that some toolchains read implicit directories from an environment variable such as LIBRARY_PATH so keep its value consistent when operating in a given build tree.

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https://cmake.org/cmake/help/v3.6/variable/CMAKE_LANG_IMPLICIT_LINK_DIRECTORIES.html