docs/zh_CN: add the translation of kbuild/llvm.rst

Finish the translation of kbuild/llvm.rst and move llvm from TODO
to the main body.

Update to commit 145082eb ("Documentation/llvm: turn make command
for ccache into code block")

Signed-off-by: Dongliang Mu <dzm91@hust.edu.cn>
Reviewed-by: Yanteng Si <si.yanteng@linux.dev>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20241023153235.1291567-1-dzm91@hust.edu.cn