Bug#1000892: cvise: Please upgrade to llvm-toolchain-12 or 13

[Peter Michael Green]

severity 1000892 serious
thanks

As part of the effort to limit the number of llvm packages in the
archive, please upgrade to -13 (or -12).
It has:
   llvm-9-dev [armel armhf], libclang-9-dev [armel armhf], clang-9 [armel 
armhf], clang-format-9 [armel armhf],
llvm-toolchain-9 has now been removed from testing, so this is now a 
violation of the rc policy
"packages must be buildable within the same release.