[llvm] [utils][filecheck-lint]: speedup filecheck_lint (PR #94191)

[via llvm-commits]

================
@@ -49,27 +49,15 @@ def test_find_potential_directives_comment_prefix(self):
         results = list(fcl.find_potential_directives(content))
         assert len(results) == 3
         pos, match = results[0]
-        assert (
-            pos.line == 1
-            and pos.start_column == len("junk; ") + 1
-            and pos.end_column == len(lines[0]) - 1
-        )
+        assert pos.as_str() == "1:7-11"
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klensy wrote:

This looks like copypaste and not maintainable - change in input lines only will break tests without fixes here too.
Maybe add comment like:
```
junk; CHCK1:
      |   |
      |   column 11
      column 7

```

https://github.com/llvm/llvm-project/pull/94191