Re-enable warning 4701 for GN build and some cleanup

xfa/fgas/localization/fgas_datetime.h

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #ifndef XFA_FGAS_LOCALIZATION_FGAS_DATETIME_H_
 #define XFA_FGAS_LOCALIZATION_FGAS_DATETIME_H_
 
 #include "core/fxcrt/include/fx_system.h"
@@ skipping 187 matching lines @@
     struct {
       uint8_t hour;
       uint8_t minute;
       uint8_t second;
       uint16_t millisecond;
     } sTime;
     FX_TIME aTime;
   } Time;
 };
 
-struct FX_DATETIMEZONE {
-  union {
-    struct {
-      union {
-        struct {
-          int32_t year;
-          uint8_t month;
-          uint8_t day;
-        };
-        FX_DATE date;
-      };
-      union {
-        struct {
-          uint8_t hour;
-          uint8_t minute;
-          uint8_t second;
-          uint16_t millisecond;
-        };
-        FX_TIME time;
-      };
-    };
-    FX_DATETIME dt;
-  };
-  union {
-    struct {
-      int8_t tzHour;
-      uint8_t tzMinute;
-    };
-    FX_TIMEZONE tz;
-  };
-};
 #if _FX_OS_ != _FX_ANDROID_
 #pragma pack(pop)
 #endif
 
 class CFX_DateTime {
  public:
   CFX_DateTime() {}
   CFX_DateTime(const FX_DATETIME& dt) { m_DateTime = dt; }
   CFX_DateTime(const CFX_DateTime& dt) { m_DateTime = dt.m_DateTime; }
   virtual ~CFX_DateTime() {}
@@ skipping 148 matching lines @@
   }
   friend FX_BOOL operator<=(const FX_DATETIME& dt1, const CFX_DateTime& dt2) {
     return ((const CFX_DateTime&)dt1).ToUnitime() <= dt2.ToUnitime();
   }
 
  private:
   FX_DATETIME m_DateTime;
 };
 
 #endif  // XFA_FGAS_LOCALIZATION_FGAS_DATETIME_H_