[llvm] [z/OS] Modify regex in error message to match on z/OS. (PR #194020)

[via llvm-commits]

================
@@ -18,7 +18,7 @@
 # CHECK: Command Output (stderr):
 # CHECK-NEXT: --
 # CHECK-NOT: --
-# CHECK: cat{{(_64)?(\.exe)?}}: {{(cannot open does-not-exist|.*does-not-exist.*: No such file or directory)}}
+# CHECK: cat{{(_64)?(\.exe)?}}: {{(cannot open does-not-exist|.*does-not-exist.*: .*No such file or directory)}}
----------------
sujianIBM wrote:

I tried that but it did not work for me.
I modified the regex to 
```
cat{{(_64)?(\.exe)?}}: {{(cannot open does-not-exist|.*does-not-exist.*: [[ERROR_MSG]])}}
```
It seems to me variables (like [[ERROR_MSG]]) do not work inside regex.

https://github.com/llvm/llvm-project/pull/194020