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

[via llvm-commits]

dyung wrote:

We are also seeing build failures in two of our bots:
 - https://lab.llvm.org/buildbot/#/builders/174/builds/21128
 - https://lab.llvm.org/buildbot/#/builders/181/builds/23904

Can you please take a look and revert if you need time to investigate?

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