Update ICU to 58.1

source/i18n/unicode/tmutfmt.h

Index: source/i18n/unicode/tmutfmt.h
diff --git a/source/i18n/unicode/tmutfmt.h b/source/i18n/unicode/tmutfmt.h
index 728ff13219a012d1c886ee98bb8d8ea183cbd18b..b90d4a096d71bbcd45cca01c4e8beba0af740d85 100644
--- a/source/i18n/unicode/tmutfmt.h
+++ b/source/i18n/unicode/tmutfmt.h
@@ -1,3 +1,5 @@
+// Copyright (C) 2016 and later: Unicode, Inc. and others.
+// License & terms of use: http://www.unicode.org/copyright.html
 /*
  *******************************************************************************
  * Copyright (C) 2008-2014, Google, International Business Machines Corporation
@@ -50,6 +52,8 @@ U_NAMESPACE_BEGIN
 class Hashtable;
 class UVector;
 
+struct TimeUnitFormatReadSink;
+
 /**
  * Format or parse a TimeUnitAmount, using plural rules for the units where available.
  *
@@ -227,6 +231,7 @@ private:
     // UTIMEUNIT_YEAR.
     static const char* getTimeUnitName(TimeUnit::UTimeUnitFields field, UErrorCode& status);
 
+    friend struct TimeUnitFormatReadSink;
 };
 
 inline UBool