[llvm] [LLVM] Change `Intrinsic::getBaseName` to return `std::string` (PR #111613)

[Rahul Joshi via llvm-commits]

jurahul wrote:

> I would think avoiding std::string allocations is more important than reducing the size of the intrinsic name table. What is the compile time impact of this?

I guess it depends on the use case. Is there some standard compile time benchmark that I can run? A micro-bench targeting `Intrinsic::getName()` (similar to what I had added in earlier commits) will I am guessing show that returning std::string is slower, but that doesn't tell much more than that, hence a broader "e2e" compile time benchmark might help qualify perf impact better.

https://github.com/llvm/llvm-project/pull/111613