[llvm] [llvm][Support] Add support for executing a detached process (PR #81708)

[Alexandre Ganea via llvm-commits]

https://github.com/aganea commented:

Would you mind please explaining what is the purpose of this change? (in the description ideally) I know it's for the LLVM CAS but I'm not sure I understand exactly what is it for.

https://github.com/llvm/llvm-project/pull/81708