CMake Nightly Date Stamp
Set the AppleClang policy.

Don't bump the required version, setting all recent policies.
Merge topic 'target_compile_features' into next

0a42151c Set the AppleClang policy.
Export: Populate INTERFACE_COMPILE_FEATURES property.
Features: Add cxx_delegating_constructors.
Features: Add cxx_variadic_templates.

Expect cxx_variadic_templates to implement N2555.

N2555 is essentially a bugfix and predates most compiler releases which
aimed to experimentally support variadic templates.
Features: Add cxx_constexpr.
Features: Add cxx_static_assert.
Features: Add cxx_final.
Features: Add cxx_override.
Features: Add cxx_auto_function.
Features: Add cxx_strong_enums.
Features: Add cxx_decltype.
Features: Add cxx_defaulted_functions.
Features: Add cxx_deleted_functions.
Features: Add cxx_explicit_conversions.
Features: Add cxx_inheriting_constructors.
Features: Add cxx_lambdas.
Features: Add cxx_nonstatic_member_init.
Features: Add cxx_noexcept.