[clang-tools-extra] [clang-doc] Refactor error handling to use ExitOnError (PR #141699)

[Samarth Narang via cfe-commits]

snarang181 wrote:

Thanks again @ilovepi for the handholding, appreciate it. 

BTW -- do you know what's going on with the Linux CI? 

https://github.com/llvm/llvm-project/pull/141699