Fix Win debug build
Windows debug build has this compile error. Try to fix it.
icu_63::uprv_detectWindowsTimeZone' should not add 'dllexport' attribute
[-Werror,-Wdll-attribute-on-redeclaration]
uprv_detectWindowsTimeZone()
diff --git a/source/common/wintz.h b/source/common/wintz.h
index f98b177..cd8565e 100644
--- a/source/common/wintz.h
+++ b/source/common/wintz.h
@@ -28,7 +28,7 @@
typedef struct _TIME_ZONE_INFORMATION TIME_ZONE_INFORMATION;
U_CDECL_END
-U_CFUNC const char* U_EXPORT2
+U_INTERNAL const char* U_EXPORT2
uprv_detectWindowsTimeZone();
#endif /* U_PLATFORM_USES_ONLY_WIN32_API */
