Explicitly pass -Wno-unused-function to the targets that need it.

third_party/yasm/yasm.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.
 
 # The yasm build process creates a slew of small C subprograms that
 # dynamically generate files at various point in the build process.  This makes
 # the build integration moderately complex.
 #
 # There are three classes of dynamically generated files:
 #   1) C source files that should be included in the build (eg., lc3bid.c)
@@ skipping 540 matching lines @@
          'source/patched-yasm/tools/re2c/substr.c',
          'source/patched-yasm/tools/re2c/translate.c',
       ],
       'include_dirs': [
         '<@(yasm_include_dirs)',
       ],
       'cflags': [
         '-std=gnu99',
       ],
       'variables': {
+        'clang_warning_flags': [
           # re2c is missing CLOSEVOP from one switch.
-        'clang_warning_flags': [ '-Wno-switch' ],
+          '-Wno-switch',
+          # re2c contains many static functions in headers (because it's
+          # a C library predating C99.)
+          '-Wno-unused-function',
+        ],
       },
       'msvs_disabled_warnings': [ 4267 ],
     },
     {
       'target_name': 'genmodule',
       'type': 'executable',
       'toolsets': ['host'],
       'dependencies': [
         'config_sources',
       ],
       'sources': [
         'source/patched-yasm/libyasm/genmodule.c',
       ],
       'include_dirs': [
         '<@(yasm_include_dirs)',
 
       ],
       'cflags': [
         '-std=gnu99',
       ],
     },
   ],
 }