Auto merge of #43008 - zackmdavis:field_init_shorthand_in_librustc, r=<try>

use field init shorthand in src/librustc/

Commentary on #37340 [suggested](#37340 (comment)) using the new field init syntax in the compiler. Do we care about this? If so, here's a pull request for the librustc/ directory. While [`rustfmt` might do this in the future](#37340 (comment)), in the meantime, some simple Python will do:

```python
#!/usr/bin/env python3

import os, re, sys

OPPORTUNITY = re.compile(r" (\w+): \1,?\n")

def field_init_shorthand_substitution(filename):
    with open(filename) as f:
        text = f.read()
        revised = OPPORTUNITY.sub(r" \1,\n", text)
    with open(filename, 'w') as f:
        f.write(revised)

def substitute_in_directory(path):
    for dirname, _subdirs, basenames in os.walk(path):
        for basename in basenames:
            field_init_shorthand_substitution(os.path.join(dirname, basename))

if __name__ == "__main__":
    substitute_in_directory(sys.argv[1])
```

**Update 3 July**: edited the search (respectively replace) regex to ` (\w+): \1,?\n` (` \1,\n`) from ` (\w+): \1,` (` \1,`)

Author: bors

src/librustc/cfg/construct.rs

@@ -58,20 +58,20 @@ pub fn construct<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     let tables = tcx.typeck_tables_of(owner_def_id);
 
     let mut cfg_builder = CFGBuilder {
-        tcx: tcx,
+        tcx,
         owner_def_id,
-        tables: tables,
-        graph: graph,
-        fn_exit: fn_exit,
+        tables,
+        graph,
+        fn_exit,
         loop_scopes: Vec::new(),
         breakable_block_scopes: Vec::new(),
     };
     body_exit = cfg_builder.expr(&body.value, entry);
     cfg_builder.add_contained_edge(body_exit, fn_exit);
     let CFGBuilder { graph, .. } = cfg_builder;
     CFG {
-        graph: graph,
-        entry: entry,
+        graph,
+        entry,
         exit: fn_exit,
     }
 }

src/librustc/dep_graph/dep_tracking_map.rs

@@ -36,7 +36,7 @@ impl<M: DepTrackingMapConfig> DepTrackingMap<M> {
     pub fn new(graph: DepGraph) -> DepTrackingMap<M> {
         DepTrackingMap {
             phantom: PhantomData,
-            graph: graph,
+            graph,
             map: FxHashMap(),
         }
     }