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

[Connor Sughrue via llvm-commits]

cpsughrue wrote:

@aganea I have pushed the unit test. If you have a chance can you let me know what you think? It looks like the CI failed due to an unrelated flang test.

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