Update ICU to 58.1

source/common/unicode/ucnv.h

Index: source/common/unicode/ucnv.h
diff --git a/source/common/unicode/ucnv.h b/source/common/unicode/ucnv.h
index 564656c284f8e0270b2c956254322b4443b30351..767c1a2a7f44f12a1c97fe32053027d00091b876 100644
--- a/source/common/unicode/ucnv.h
+++ b/source/common/unicode/ucnv.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) 1999-2014, International Business Machines
@@ -941,8 +943,13 @@ typedef enum UConverterUnicodeSet {
     UCNV_ROUNDTRIP_SET,
     /** Select the set of Unicode code points with roundtrip or fallback mappings. @stable ICU 4.0 */
     UCNV_ROUNDTRIP_AND_FALLBACK_SET,
-    /** Number of UConverterUnicodeSet selectors. @stable ICU 2.6 */
+#ifndef U_HIDE_DEPRECATED_API
+    /**
+     * Number of UConverterUnicodeSet selectors.
+     * @deprecated ICU 58 The numeric value may change over time, see ICU ticket #12420.
+     */
     UCNV_SET_COUNT
+#endif  // U_HIDE_DEPRECATED_API
 } UConverterUnicodeSet;