Use IndexVec::from_raw to construct a const IndexVec.

Author: nnethercote

compiler/rustc_mir_transform/src/shim.rs

@@ -404,8 +404,7 @@ fn build_thread_local_shim<'tcx>(
 let span = tcx.def_span(def_id);
 let source_info = SourceInfo::outermost(span);
 
-letmut blocks = IndexVec::with_capacity(1);
- blocks.push(BasicBlockData{
+let blocks = IndexVec::from_raw(vec![BasicBlockData{
  statements: vec![Statement{
  source_info,
  kind:StatementKind::Assign(Box::new((
@@ -415,7 +414,7 @@ fn build_thread_local_shim<'tcx>(
 }],
  terminator:Some(Terminator{ source_info, kind:TerminatorKind::Return}),
  is_cleanup:false,
-});
+}]);
 
 new_body(
 MirSource::from_instance(instance),