[llvm] [lit] Add an option to read an xfail list from a file (PR #163959)

[David Spickett via llvm-commits]

================
@@ -356,6 +360,10 @@ The timing data is stored in the `test_exec_root` in a file named
   primary purpose is to suppress an ``XPASS`` result without modifying a test
   case that uses the ``XFAIL`` directive.
 
+.. option:: --xfail-not-from-file PATH
+
+  Read a line separated list of tests from a file to be used by :option:`--xfail-not`.
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DavidSpickett wrote:

Saying it's used by the option is detail that users don't really need. What they might want to know is that this option does add to that other one. So you could say:
```
Acts as --xfail-not, except that the paths are read from the specified file. If this option and --xfail-not are specified at the same time, both sets of paths are considered.
```
Then you're also going back to the "this option but from a file" idea that you stated in the PR description.

https://github.com/llvm/llvm-project/pull/163959