在这里我找到了如何安装 clang3.8 的说明：http ://llvm.org/apt/
所以我执行了：
wget -O - http://llvm.org/apt/llvm-snapshot.gpg.key|sudo apt-key add -
结果：
--2015-09-19 12:53:09-- http://llvm.org/apt/llvm-snapshot.gpg.key
Resolving llvm.org (llvm.org)... [sudo] password for user: 192.17.58.186
Connecting to llvm.org (llvm.org)|192.17.58.186|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 3145 (3,1K) [application/pgp-keys]
Saving to: ‘STDOUT’
100%[======================================>] 3.145 --.-K/s in 0,002s
2015-09-19 12:53:10 (1,87 MB/s) - written to stdout [3145/3145]
OK
进而：
sudo apt-get install clang-3.8 clang-3.8-doc libclang-common-3.8-dev libclang-3.8-dev libclang1-3.8 libclang1-3.8-dbg libllvm-3.8-ocaml-dev libllvm3.8 libllvm3.8-dbg lldb-3.8 llvm-3.8 llvm-3.8-dev llvm-3.8-doc llvm-3.8-examples llvm-3.8-runtime clang-modernize-3.8 clang-format-3.8 …