Set the cmake policy for CMP0066 and CMP0067

[tannergooding]

As per https://cmake.org/cmake/help/v3.21/policy/CMP0066.html and https://cmake.org/cmake/help/v3.21/policy/CMP0067.html, the default policy for these is OLD meaning that try_compile checks (such as is done for check_c_source_compiles) will not respect CMAKE_<LANG>_FLAGS, CMAKE_<LANG>_STANDARD, CMAKE_<LANG>_STANDARD_REQUIRED, and CMAKE_<LANG>_EXTENSIONS variables.

The net effect of this is that certain header or other checks may be misreported between the test and what we ultimately compile our source with and may cause less efficient code or other downstream failures such as #56746.

This resolves#56746 by ensuring that these policies are explicitly set to NEW so that the cmake tests match our source compilation configuration and are accurate.

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Issue Details

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As per https://cmake.org/cmake/help/v3.21/policy/CMP0066.html and https://cmake.org/cmake/help/v3.21/policy/CMP0067.html, the default policy for these is OLD meaning that try_compile checks (such as is done for check_c_source_compiles) will not respect CMAKE_<LANG>_FLAGS, CMAKE_<LANG>_STANDARD, CMAKE_<LANG>_STANDARD_REQUIRED, and CMAKE_<LANG>_EXTENSIONS variables.

The net effect of this is that certain header or other checks may be misreported between the test and what we ultimately compile our source with and may cause less efficient code or other downstream failures such as #56746.

This resolves #56746 by ensuring that these policies are explicitly set to NEW so that the cmake tests match our source compilation configuration and are accurate.

Author:	tannergooding
Assignees:	-
Labels:	area-Infrastructure-coreclr
Milestone:	-

[tannergooding]

@jkoritzinsky, any other sign-off needed here or can we merge?

[jkoritzinsky]

I think we can merge this