[compiler-rt] [libfuzzer] Prevent MSan false positive when printing log with -jobs (PR #91679)

[Evgenii Stepanov via llvm-commits]

eugenis wrote:

This looks reasonable, but I wonder if it would be safer to move the scoped-disable thing to the start of WorkerThread?  The thread does not run any user code, so we never want any interceptor checks (and it may run some other interceptors, like fork/exec, mutex stuff, etc).

https://github.com/llvm/llvm-project/pull/91679