Fix build on fedora 26

Author: NathanW2

src/auth/oauth2/qgsauthoauth2config.cpp

@@ -11,6 +11,7 @@
  *   (at your option) any later version.                                   *
  *                                                                         *
  ***************************************************************************/
+#include <functional>
 
 #include "qgsauthoauth2config.h"
 

src/core/geometry/qgsabstractgeometry.h

@@ -16,6 +16,8 @@ email                : marco.hugentobler at sourcepole dot com
 #ifndef QGSABSTRACTGEOMETRYV2
 #define QGSABSTRACTGEOMETRYV2
 
+#include <functional>
+
 #include <QString>
 
 #include "qgis_core.h"

src/core/geometry/qgsgeometry.h

@@ -16,6 +16,8 @@ email                : morb at ozemail dot com dot au
 #ifndef QGSGEOMETRY_H
 #define QGSGEOMETRY_H
 
+#include <functional>
+
 #include <QDomDocument>
 #include <QSet>
 #include <QString>

src/core/geometry/qgsinternalgeometryengine.h

@@ -18,6 +18,8 @@
 
 #define SIP_NO_FILE
 
+#include <functional>
+
 #include "qgspointxy.h"
 
 class QgsGeometry;

src/providers/wfs/qgswfsrequest.h

@@ -15,6 +15,8 @@
 #ifndef QGSWFSREQUEST_H
 #define QGSWFSREQUEST_H
 
+#include <functional>
+
 #include <QObject>
 #include <QNetworkRequest>
 #include <QNetworkReply>