Fix new ? inference errors in librustc_mir

Author: cuviper

src/librustc_mir/hair/constant.rs

@@ -17,7 +17,7 @@ crate fn lit_to_const<'a, 'gcx, 'tcx>(
 ) -> Result<ty::Const<'tcx>, LitToConstError> {
     use syntax::ast::*;
 
-    let trunc = |n| {
+    let trunc = |n| -> Result<_, LitToConstError> {
         let param_ty = ParamEnv::reveal_all().and(tcx.lift_to_global(&ty).unwrap());
         let width = tcx.layout_of(param_ty).map_err(|_| LitToConstError::Reported)?.size;
         trace!("trunc {} with size {} and shift {}", n, width.bits(), 128 - width.bits());