cg_llvm: stop identifying ADTs in LLVM IR
This is an extension of https://github.com/rust-lang/rust/pull/94107. It may be a minor perf win.
Fixes#96242.
Now that we use opaque pointers, ADTs can no longer be recursive, so we
do not need to name them. Previously, this would be necessary if you had
a struct like
```rs
struct Foo(Box<Foo>, u64, u64);
```
which would be represented with something like
```ll
%Foo = type { %Foo*, i64, i64 }
```
which is now just
```ll
{ ptr, i64, i64 }
```
r? `@tmiasko`
73dc6f03a2