Bug#946761: llvm-9-dev: symlinks to but doesn't depend on libclang-cpp9

[Rebecca N. Palmer]

Package: llvm-9-dev
Version: 1:9.0.0-4
Control: tags -1 patch

llvm-9-dev provides symlinks for both libclang-cpp.so (libclang-cpp9) 
and libclang.so (libclang1-9), but depends on libclang1-9 and not 
libclang-cpp9.