Build icu with -Wno-unused-function.

icu.gyp

 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   'includes': [
     'icu.gypi',
   ],
   'variables': {
     'use_system_icu%': 0,
@@ skipping 281 matching lines @@
               # enum (e.g. URES_TABLE32 which is in UResInternalType). This
               # is on purpose.
               '-Wno-switch',
               # ICU has some code with the pattern:
               #   if (found = uprv_getWindowsTimeZoneInfo(...))
               '-Wno-parentheses',
               # ICU generally has no unused variables, but there are a few
               # places where this warning triggers.
               # See https://codereview.chromium.org/1222643002/ and
               # http://www.icu-project.org/trac/ticket/11759.
-              "-Wno-unused-const-variable",
+              '-Wno-unused-const-variable',
+              # ucnv2022.cpp contains three functions that are only used when
+              # certain preprocessor defines are set.
+              '-Wno-unused-function',
             ],
           },
           'cflags': [
             # Since ICU wants to internally use its own deprecated APIs,
             # don't complain about it.
             '-Wno-deprecated-declarations',
             '-Wno-unused-function',
           ],
           'cflags_cc': [
             '-frtti',
@@ skipping 283 matching lines @@
           },
           'includes': [
             '../../build/shim_headers.gypi',
           ],
           'toolsets': ['target'],
         },
       ], # targets
     }],
   ], # conditions
 }