[clang] [LifetimeSafety] Add language option for experimental lifetime safety (PR #149592)

[Sjoerd Meijer via cfe-commits]

sjoerdmeijer wrote:

Hello, I am a `-Weverything` user, but not an expert...
First #148222 broke my build. I understood and experimental feature was enabled under `-Weverything`.
This patch and fix improved things and I see less build failures, but my problems haven't gone away. 
Now Clang hangs compiling some files, it doesn't terminate. 

Could some experimental features still be enabled? Or do you think this is something else? Do you have some advice?

https://github.com/llvm/llvm-project/pull/149592