GN: Don't explicitly define __ANDROID__ now that clang defines it automatically

build/config/compiler/BUILD.gn

 # Copyright (c) 2013 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.
 
 import("//build/config/android/config.gni")
 import("//build/config/chrome_build.gni")
 if (current_cpu == "arm") {
   import("//build/config/arm.gni")
 }
 if (current_cpu == "mipsel" || current_cpu == "mips64el") {
@@ skipping 541 matching lines @@
     }
     if (is_asan) {
       # Android build relies on -Wl,--gc-sections removing unreachable code.
       # ASan instrumentation for globals inhibits this and results in a library
       # with unresolvable relocations.
       # TODO(eugenis): find a way to reenable this.
       cflags += [ "-mllvm -asan-globals=0" ]
     }
 
     defines += [ "ANDROID" ]
-    if (is_clang) {
-      # GCC provides this as a built-in macro, but clang does not.
-      defines += [ "__ANDROID__" ]
-    }
 
     # The NDK has these things, but doesn't define the constants
     # to say that it does. Define them here instead.
     defines += [ "HAVE_SYS_UIO_H" ]
 
     # Use gold for Android for most CPU architectures.
     if (current_cpu == "x86" || current_cpu == "x64" || current_cpu == "arm") {
       ldflags += [ "-fuse-ld=gold" ]
       if (is_clang) {
         # Let clang find the ld.gold in the NDK.
@@ skipping 760 matching lines @@
       cflags += [ "-gsplit-dwarf" ]
     }
   }
 }
 
 config("no_symbols") {
   if (!is_win) {
     cflags = [ "-g0" ]
   }
 }