This fixes compiling things like the `snap` crate after https://reviews.llvm.org/D105462. I added a test that verifies the additional attribute gets specified, and confirmed that I can build cargo with both LLVM 13 and 14 with this change applied.
fn_abi_of_{fn_ptr,instance}
abi::Abi
Copy
decl
FnAbi::llvm_type
LayoutOf
ty::layout