Add a variable to indicate the latest standard known to be supported for
each language:
* `CMAKE_C_STANDARD_LATEST`
* `CMAKE_CXX_STANDARD_LATEST`
* `CMAKE_CUDA_STANDARD_LATEST`
* `CMAKE_HIP_STANDARD_LATEST`
* `CMAKE_OBJC_STANDARD_LATEST`
* `CMAKE_OBJCXX_STANDARD_LATEST`
These variables, more generally referred to as
`CMAKE_<LANG>_STANDARD_LATEST`, are assigned an integer value which
represents the minimum between the latest version of the associated
language standard supported by the current compiler and the latest
version supported by CMake.
Add documentation for these variables in a new page called
`CMAKE_<LANG>_STANDARD_LATEST` was added under the "Variables for
Languages" section of the `cmake-variables(7)` page.
Update each compiler-specific CMake script under
`${CMAKE_ROOT}\Modules\Compiler` to manually define the relevant
`CMAKE_<LANG>_STANDARD_LATEST` variable as necessary. This will
require updating and maintaining as newer compiler versions become
recognized by CMake.
Closes: #25717
Identify the compilers as `NVHPC` to distinguish it from the older PGI
compilers from which they evolved, and from other `NVIDIA` compilers.
Fixes: #20887
