[llvm] [OrcJIT] distinguish normal and abrupt TaskDispatcher shutdown (PR #154356)

[Jameson Nash via llvm-commits]

vtjnash wrote:

I didn't touch anything related to the CI segfault during parsing, so that is not my fault.
```
2025-08-19T15:30:57.5623655Z # executed command: 'c:\_work\llvm-project\llvm-project\build\bin\clang.exe' -cc1 -internal-isystem 'C:\_work\llvm-project\llvm-project\build\lib\clang\22\include' -nostdsysteminc -fsyntax-only -std=c++17 -pedantic -verify 'C:\_work\llvm-project\llvm-project\clang\test\SemaCXX\cxx17-compat.cpp'
```

https://github.com/llvm/llvm-project/pull/154356