Honor language standard in try_compile() source-file signature.

The try_compile() source file signature is intended to allow callers to check whether they will be able to compile a given source file with the current toolchain. In order to match compiler behavior, any language standard mode should match. However, CMake 3.7 and below did not do this. CMake 3.8 and above prefer to honor the language standard settings for C, CXX (C++), and CUDA using the values of the variables:

This policy provides compatibility for projects that do not expect the language standard settings to be used automatically.

The OLD behavior of this policy is to ignore language standard setting variables when generating the try_compile test project. The NEW behavior of this policy is to honor language standard setting variables.

This policy was introduced in CMake version 3.8. Unlike most policies, CMake version 3.18.4 does not warn by default when this policy is not set and simply uses OLD behavior. See documentation of the CMAKE_POLICY_WARNING_CMP0067 variable to control the warning.


The OLD behavior of a policy is deprecated by definition and may be removed in a future version of CMake.