[llvm] Reapply: [lit] Avoid multiprocessing for -j1 runs (PR #179824)

[Henrik G. Olsson via llvm-commits]

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@@ -436,8 +436,11 @@ def killProcessAndChildren(pid):
             for child in children_iterator:
                 try:
                     child.kill()
-                except psutil.NoSuchProcess:
+                except psutil.Error:
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hnrklssn wrote:

The only subtypes of Error are NoSuchProcess, AccessDenied and TimeoutExpired, so this change looks fine to me. Do we want to emit a note or warning when this happens?

https://github.com/llvm/llvm-project/pull/179824