Fix -Wmicrosoft-unqualified-friend warning.

source/common/unicode/unistr.h

 /*
 **********************************************************************
 *   Copyright (C) 1998-2013, International Business Machines
 *   Corporation and others.  All Rights Reserved.
 **********************************************************************
 *
 * File unistr.h
 *
 * Modification History:
 *
@@ skipping 16 matching lines @@
  */
 
 #include "unicode/utypes.h"
 #include "unicode/rep.h"
 #include "unicode/std_string.h"
 #include "unicode/stringpiece.h"
 #include "unicode/bytestream.h"
 #include "unicode/ucasemap.h"
 
 struct UConverter;          // unicode/ucnv.h
-class  StringThreadTest;
 
 #ifndef U_COMPARE_CODE_POINT_ORDER
 /* see also ustring.h and unorm.h */
 /**
  * Option bit for u_strCaseCompare, u_strcasecmp, unorm_compare, etc:
  * Compare strings in code point order instead of code unit order.
  * @stable ICU 2.2
  */
 #define U_COMPARE_CODE_POINT_ORDER  0x8000
 #endif
@@ skipping 3436 matching lines @@
     kOpenGetBuffer=16,  // getBuffer(minCapacity) was called (is "open"),
                         // and releaseBuffer(newLength) must be called
 
     // combined values for convenience
     kShortString=kUsingStackBuffer,
     kLongString=kRefCounted,
     kReadonlyAlias=kBufferIsReadonly,
     kWritableAlias=0
   };
 
-  friend class StringThreadTest;
   friend class UnicodeStringAppendable;
 
   union StackBufferOrFields;        // forward declaration necessary before friend declaration
   friend union StackBufferOrFields; // make US_STACKBUF_SIZE visible inside fUnion
 
   /*
    * The following are all the class fields that are stored
    * in each UnicodeString object.
    * Note that UnicodeString has virtual functions,
    * therefore there is an implicit vtable pointer
@@ skipping 956 matching lines @@
 { return doReverse(0, length()); }
 
 inline UnicodeString&
 UnicodeString::reverse(int32_t start,
                int32_t _length)
 { return doReverse(start, _length); }
 
 U_NAMESPACE_END
 
 #endif