codegen_llvm: avoid Deref impls w/ extern type

`rustc_codegen_llvm` relied on `Deref` impls where `Deref::Target` was
or contained an extern type - in my experimental implementation of
rust-lang/rfcs#3729, this isn't possible as the `Target` associated
type's `?Sized` bound cannot be relaxed backwards compatibly (unless we
come up with some way of doing this).

In later pull requests with the rust-lang/rfcs#3729 implementation,
breakage like this could only occur for nightly users relying on the
`extern_types` feature.

Upstreaming this to avoid needing to keep carrying this patch locally,
and I think it'll necessarily need to change eventually.

compiler/rustc_codegen_llvm/src/common.rs

@@ -77,7 +77,7 @@ impl<'ll> Funclet<'ll> {
     }
 
     pub(crate) fn bundle(&self) -> &llvm::OperandBundle<'ll> {
-        &self.operand
+        self.operand.raw()
     }
 }