Use associative type defaults in {Layout,FnAbi}OfHelpers.

This avoids some repetitive boilerplate code.

compiler/rustc_codegen_llvm/src/builder.rs

@@ -93,8 +93,6 @@ impl HasTargetSpec for Builder<'_, '_, '_> {
 }
 
 impl<'tcx> LayoutOfHelpers<'tcx> for Builder<'_, '_, 'tcx> {
-    type LayoutOfResult = TyAndLayout<'tcx>;
-
     #[inline]
     fn handle_layout_err(&self, err: LayoutError<'tcx>, span: Span, ty: Ty<'tcx>) -> ! {
         self.cx.handle_layout_err(err, span, ty)
@@ -102,8 +100,6 @@ impl<'tcx> LayoutOfHelpers<'tcx> for Builder<'_, '_, 'tcx> {
 }
 
 impl<'tcx> FnAbiOfHelpers<'tcx> for Builder<'_, '_, 'tcx> {
-    type FnAbiOfResult = &'tcx FnAbi<'tcx, Ty<'tcx>>;
-
     #[inline]
     fn handle_fn_abi_err(
         &self,