[llvm] [NFC][sancov] Move tests into target-specific subdirectories (PR #182111)

[Hubert Tong via llvm-commits]

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@@ -0,0 +1,4 @@
+# These tests require a registered x86 backend.
+
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hubert-reinterpretcast wrote:

Comment is wrong. Can just remove it because such `lit.local.cfg` files in target-specific test directories is common.

```suggestion
```

https://github.com/llvm/llvm-project/pull/182111