Fix for Android GN build.

BUILD.gn

 # Copyright 2014 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.
 
 config("hunspell_config") {
   defines = [
     "HUNSPELL_STATIC",
     "HUNSPELL_CHROME_CLIENT",
     "USE_HUNSPELL",
   ]
@@ skipping 63 matching lines @@
   }
 
   if (is_posix && !is_mac) {
     cflags += [
       "-Wno-unused-value",
       "-Wno-unused-variable",
       "-Wno-write-strings",
     ]
   }
 
-  if (is_linux) {
+  if (is_posix && !is_mac && !is_ios) {
     cflags += [
       # affentry.hxx has NULL as default parameter for a FLAG in two
       # places.
       "-Wno-conversion-null",
     ]
   }
 
   if (is_clang) {
     cflags += [
       # affentry.cxx has one `while ((p = nextchar(p)));` parsing loop.
       "-Wno-empty-body",
       # affentry.hxx has NULL as default parameter for a FLAG in two
       # places.
       "-Wno-null-conversion",
     ]
   }
 }