[llvm] [Tablegen] Add keyword `dump`. (PR #68793)

[Francesco Petrogalli via llvm-commits]

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@@ -1275,6 +1275,23 @@ be nested.
 This loop defines records named ``R0``, ``R1``, ``R2``, and ``R3``, along
 with ``F0``, ``F1``, ``F2``, and ``F3``.
 
+``dump`` --- print messages to stderr
+-------------------------------------
+
+A ``dump`` statement prints the input string to standard error
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fpetrogalli wrote:

Done, docs updated. 

https://github.com/llvm/llvm-project/pull/68793