MLIR: fix constant tablegen

[wsmoses]

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[Copilot]

Pull Request Overview

This PR updates the constant tablegen logic by suppressing an unused-variable warning and loosening a restriction on vector constants.

• Adds a void cast for the vectorized flag in generated code to prevent compiler warnings.
• Removes the assert(!isVec); check to allow vector constants.
• (Implicitly) broadens constant handling to include vectorized cases.

Comments suppressed due to low confidence (2)

enzyme/tools/enzyme-tblgen/enzyme-tblgen.cpp:624

• With the assert(!isVec) removed, vector constants are now allowed but no handling is provided; add explicit logic or an error path for isVec == true to avoid silent incorrect behavior.

assert(!isVec);

enzyme/tools/enzyme-tblgen/enzyme-tblgen.cpp:622

• Consider adding unit tests for cases where isVec is true to verify that vector constant handling works correctly now that the restriction has been lifted.

auto [ord1, isVec, ext, isva] = nameToOrdinal.lookup(name, pattern, resultTree);