Don't special-case llvm.* as nounwind

Certain LLVM intrinsics, such as `llvm.wasm.throw`, can unwind. Marking
them as nounwind causes us to skip cleanup of locals and optimize out
`catch_unwind` under inlining or when `llvm.wasm.throw` is used directly
by user code.

The motivation for forcibly marking llvm.* as nounwind is no longer
present: most intrinsics are linked as `extern "C"` or other
non-unwinding ABIs, so we won't codegen `invoke` for them anyway.

compiler/rustc_codegen_ssa/src/codegen_attrs.rs

@@ -511,15 +511,6 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
         err.emit();
     }
 
-    // Any linkage to LLVM intrinsics for now forcibly marks them all as never
-    // unwinds since LLVM sometimes can't handle codegen which `invoke`s
-    // intrinsic functions.
-    if let Some(name) = &codegen_fn_attrs.link_name
-        && name.as_str().starts_with("llvm.")
-    {
-        codegen_fn_attrs.flags |= CodegenFnAttrFlags::NEVER_UNWIND;
-    }
-
     if let Some(features) = check_tied_features(
         tcx.sess,
         &codegen_fn_attrs