[FailureDiagnostic] Make getConstraintLocator const

Author: theblixguy

lib/Sema/CSDiagnostics.h

@@ -149,7 +149,7 @@ class FailureDiagnostic {
   /// path, uniqued and automatically calculate the summary flags
   ConstraintLocator *
   getConstraintLocator(Expr *anchor,
-                       ArrayRef<ConstraintLocator::PathElement> path) {
+                       ArrayRef<ConstraintLocator::PathElement> path) const {
     return CS.getConstraintLocator(anchor, path);
   }
 

lib/Sema/ConstraintSystem.h

@@ -1892,7 +1892,7 @@ class ConstraintSystem {
   /// path, uniqued and automatically infer the summary flags
   ConstraintLocator *
   getConstraintLocator(Expr *anchor,
-                       ArrayRef<ConstraintLocator::PathElement> path) const;
+                       ArrayRef<ConstraintLocator::PathElement> path);
 
   /// Retrieve the constraint locator for the given anchor and
   /// an empty path, uniqued.