Auto merge of #142521 - sayantn:simplify-intrinsics, r=nikic,workingjubilee

Use `LLVMIntrinsicGetDeclaration` to completely remove the hardcoded intrinsics list

Follow-up to rust-lang/rust#142259

This also needs a rustc-perf run, because `Intrinsic::getType` can be expensive

`@rustbot` label A-LLVM A-codegen T-compiler
r? `@workingjubilee`
cc `@nikic`

Author: bors