[llvm] TableGen: Allow defining sets of runtime libraries (PR #144978)

[Matt Arsenault via llvm-commits]

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@@ -0,0 +1,27 @@
+//===- SetTheory.td - DAG set operator declarations --------*- tablegen -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// FIXME: This is not used everywhere, and different files declare
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arsenm wrote:

Declaring the recognized dag operators. These have always been "forward declared" in tablegen, but that's not actually a feature tablegen has

https://github.com/llvm/llvm-project/pull/144978