This variable controls whether the CMAKE_FIND_ROOT_PATH and CMAKE_SYSROOT are used by find_file() and find_path().
If set to ONLY, then only the roots in CMAKE_FIND_ROOT_PATH will be searched. If set to NEVER, then the roots in CMAKE_FIND_ROOT_PATH will be ignored and only the host system root will be used. If set to BOTH, then the host system paths and the paths in CMAKE_FIND_ROOT_PATH will be searched.
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© 2000–2011 Insight Software Consortium
Licensed under the BSD 3-clause License.
https://cmake.org/cmake/help/v3.7/variable/CMAKE_FIND_ROOT_PATH_MODE_INCLUDE.html