[llvm] Reland [CGData] llvm-cgdata #89884 (PR #101461)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

Why isn't this just put inside llvm/tools/llvm-cgdata/lib ? See llvm/tools/llvm-exegesis for an example of the lib being separated from the tool.

https://github.com/llvm/llvm-project/pull/101461