Fix clippy::needless_borrow in the compiler

`x clippy compiler -Aclippy::all -Wclippy::needless_borrow --fix`.

Then I had to remove a few unnecessary parens and muts that were exposed
now.

compiler/rustc_codegen_llvm/src/abi.rs

@@ -493,7 +493,7 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
             PassMode::Cast { cast, pad_i32: _ } => {
                 cast.attrs.apply_attrs_to_callsite(
                     llvm::AttributePlace::ReturnValue,
-                    &bx.cx,
+                    bx.cx,
                     callsite,
                 );
             }