Read-only indication of whether a target is IMPORTED.
The boolean value of this property is True for targets created with the IMPORTED option to add_executable() or add_library(). It is False for targets built within the project.
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© 2000–2011 Insight Software Consortium
Licensed under the BSD 3-clause License.
https://cmake.org/cmake/help/v3.7/prop_tgt/IMPORTED.html