Update ICU to 58.1

source/common/unicode/umachine.h

Index: source/common/unicode/umachine.h
diff --git a/source/common/unicode/umachine.h b/source/common/unicode/umachine.h
index 939a11706ad2dfa7ff789ba011b3e1a9a4eea37e..51581c7dcdc187120105481dbbcbab1a06aaf044 100644
--- a/source/common/unicode/umachine.h
+++ b/source/common/unicode/umachine.h
@@ -1,3 +1,5 @@
+// Copyright (C) 2016 and later: Unicode, Inc. and others.
+// License & terms of use: http://www.unicode.org/copyright.html
 /*
 ******************************************************************************
 *
@@ -49,6 +51,29 @@
  */
 #include <stddef.h>
 
+#ifndef U_HIDE_INTERNAL_API
+/*
+ *  U_USE_CHAR16_T
+ *     When defined, force use of char16_t for UChar.
+ *     Note: char16_t is expected to become the default and required in the future,
+ *           and this option will be removed.
+ *     @internal
+ */
+#ifdef U_USE_CHAR16_T
+#ifdef UCHAR_TYPE
+#undef UCHAR_TYPE
+#endif
+#define UCHAR_TYPE char16_t
+
+/*
+ * In plain C, <uchar.h> is needed for the definition of char16_t
+ */
+#ifndef __cplusplus
+#include <uchar.h>
+#endif
+#endif
+#endif  /* U_HIDE_INTERNAL_API */
+
 /*==========================================================================*/
 /* For C wrappers, we use the symbol U_STABLE.                                */
 /* This works properly if the includer is C or C++.                         */