[clang] Frontend: Define __SANITIZE_*__ macros for certain sanitizers. (PR #153888)

[Peter Collingbourne via cfe-commits]

pcc wrote:

> LGTM if formatted properly.
> 
> Is there some record of this conversation? If not, could you summarize the rationale somewhere?

Added to commit message.

https://github.com/llvm/llvm-project/pull/153888