Compilers may implement this by implementing a `_cmake_cxx_import_std`
function which takes the standard version as an argument (e.g., `23`)
and creating a target named `CMake::CXX${std}` that represents how
`import std;` should be represented within CMake.
Previously compilers that had full support for a language standard level
were still verified every time a new build directory was created. Now
we record this information and insert the correct granular compile
features instead of doing a `try_compile`.
Previously compilers that had full support for a language
standard level was forced to verify this every time a new build
directory was created. Now we record this information and insert
the correct granular compile features instead of doing a try_compile.
Add default implementations for the cmake_record_lang_compile_features
macros. All implementations of this are the same so it can be safely
factored out to a common implementation.
With numerous compilers now supporting multiple language standards in CMake,
some common design patterns have begun to emerge. This is intended to
be a collection of macros implementing many of those common design
patterns that can be factored out and leveraged by many compilers.
Currently this only contains the code to set the default language
standard of not preset. More functionality will be added in the future
as appropriate.
