[llvm] RuntimeLibcalls: Mostly move x86 configuration into tablegen (PR #148575)

[Matt Arsenault via llvm-commits]

arsenm wrote:

### Merge activity

* **Jul 15, 7:17 AM UTC**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/148575).


https://github.com/llvm/llvm-project/pull/148575