Tasking compiler extensions and language standard flags are not tied
together as they are with gcc/clang. Since CMake does not model
granular abstractions for extensions, leave individual extension flags
to the project or user.
Fixes: #26591
In commit 94df5b6ef1 (Tasking: Add support for several compiler
toolsets, 2022-07-20, v3.25.0-rc1~133^2) the extension mode flags were
added with an extra space-only argument. Remove it. Also fix the C++98
mode flag that looks like a C mode flag.
Fixes: #26244
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
