Share span lookup across both cxx defn xref results

Summary:
Slight optimization. We were computing the span twice, once for the decl -> def target, and against for the def -> decl target.

Just do it once outside the loop.

Reviewed By: nhawkes

Differential Revision: D39414932

fbshipit-source-id: ea5047ed9b09cedded3c1bd17e59fac0b98e694b

glean/schema/py/symbolidcxx.py

@@ -2,6 +2,7 @@
 # To regenerate this file run fbcode//glean/schema/gen/sync
 from typing import Optional, Tuple, Union, List, Dict, TypeVar
 from thrift.py3 import Struct
+from enum import Enum
 import ast
 from glean.schema.py.glean_schema_predicate import GleanSchemaPredicate, angle_for, R, Just, InnerGleanSchemaPredicate
 from glean.schema.py.cxx1 import *

glean/schema/source/codemarkup.cxx.angle

@@ -207,12 +207,12 @@ predicate CxxFileEntityTraceDeclToDefXRefLocations:
   { File, Trace, XRef, Entity } where
     Trace = cxx1.Trace { File, cxx1.Declarations Decls, _ };
     Decl = Decls[..];
+    cxx1.DeclarationNameSpan { Decl, _, Span };
     # Get xrefs from decl to defn ,and defn back to decl family
     ({ Entity, Location } where
       CxxDeclToDefXRefTargetLocation { Decl, Entity, Location } |
       CxxDefToDeclFamilyXRefTargetLocation { Decl, Entity, Location }
     );
-    cxx1.DeclarationNameSpan { Decl, _, Span };
     { Location, { span = Span }} = XRef;
 
 # For a given Decl, it might have a base Defn, build an entity for that