[llvm] [AIX] Fix AIX failures due to switch to internal shell (PR #160566)

[David Tenty via llvm-commits]

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@@ -11,7 +11,7 @@
 
 # CHECK-LABEL: FAIL: shtest-readfile :: file-does-not-exist.txt ({{[^)]*}})
 # CHECK: echo $(cat /file/does/not/exist) && test -e /file/does/not/exist {{.*}}
-# CHECK: cat: /file/does/not/exist: No such file or directory
+# CHECK: {{.*}}cat{{.*}}/file/does/not/exist{{.*}}
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daltenty wrote:

nit: it would have been nice if this checked an exit code or something less fragile, but I guess this is what the existing test was doing 😅

https://github.com/llvm/llvm-project/pull/160566