[libc] [flang] [compiler-rt] [clang-tools-extra] [llvm] [clang] [flang] use setsid to assign the child to prevent zombie as it will be clean up by init process (PR #77944)

[Kiran Chandramohan via cfe-commits]

kiranchandramohan wrote:

Could you add a test?

https://github.com/llvm/llvm-project/pull/77944