[llvm] TableGen: Use StringOffsetTable for RuntimeLibcall names (PR #148839)

[Matt Arsenault via llvm-commits]

arsenm wrote:

### Merge activity

* **Jul 15, 2:13 PM UTC**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/148839).


https://github.com/llvm/llvm-project/pull/148839