CMP0056

Honor link flags in try_compile() source-file signature.

The try_compile() command source-file signature generates a CMakeLists.txt file to build the source file into an executable. In order to compile the source the same way as it might be compiled by the calling project, the generated project sets the value of the CMAKE_<LANG>_FLAGS variable to that in the calling project. The value of the CMAKE_EXE_LINKER_FLAGS variable may be needed in some cases too, but CMake 3.1 and lower did not set it in the generated project. CMake 3.2 and above prefer to set it so that linker flags are honored as well as compiler flags. This policy provides compatibility with the pre-3.2 behavior.

The OLD behavior for this policy is to not set the value of the CMAKE_EXE_LINKER_FLAGS variable in the generated test project. The NEW behavior for this policy is to set the value of the CMAKE_EXE_LINKER_FLAGS variable in the test project to the same as it is in the calling project.

If the project code does not set the policy explicitly, users may set it on the command line by defining the CMAKE_POLICY_DEFAULT_CMP0056 variable in the cache.

This policy was introduced in CMake version 3.2. Unlike most policies, CMake version 3.19.0-rc3 does not warn by default when this policy is not set and simply uses OLD behavior. See documentation of the CMAKE_POLICY_WARNING_CMP0056 variable to control the warning.