Codegen Overloaded LLVM intrinsics based on their name

[sayantn]

This is a continuation of #140763 - now codegenning overloaded LLVM intrinsics based on their name too. This PR parses the link_name of the LLVM intrinsics for the type parameters, partially inverting getMangledTypeStr and getIntrinsicNameImpl from LLVM.

There is the concern that @nikic's work on LLVM intrinsics might remove the name mangling, but we can just retain that from the Rust side. I mean even though the LLVM IR wouldn't have the mangling, but we can require that the Rust link_name argument contain the mangling. This shouldn't break anything, as existing code already has the name mangling.

I prefer this approach over the IITDesc approach highlighted in #140763 because this approach allows code like

#[link_name = "llvm.sqrt.v8bf16"]
fn foo(a: u16x8) -> u16x8;

which pairs up with the autocasts of #140763 to give a nice way to call overloaded intrinsics on bf16. Also this approach is a lot less work and more resilient to LLVM changes than the IITDesc approach.

One important change - the parsing doesn't account for LLVM typed pointers, which were deprecated in LLVM15 and removed in LLVM17, so I didn't bother putting support for them. So, I also removed all uses of typed pointers from the tree.

r? @dianqk as you might have more of a context on this due to reviewing the last 2 PRs
cc @nikic

[rustbot]

Some changes occurred to the intrinsics. Make sure the CTFE / Miri interpreter
gets adapted for the changes, if necessary.

cc @rust-lang/miri, @RalfJung, @oli-obk, @lcnr

The Rustfmt subtree was changed

cc @rust-lang/rustfmt