android: Make 64-bit chromes compile with clang.

build/config/android/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.
 
 import("//build/config/android/config.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 
 assert(is_android)
 
 # This is included by reference in the //build/config/compiler config that
@@ skipping 45 matching lines @@
     # http://crbug.com/448386
     "-Wl,--exclude-libs=libvpx_assembly_arm.a",
   ]
 
   if (is_clang) {
     if (current_cpu == "arm") {
       abi_target = "arm-linux-androideabi"
     } else if (current_cpu == "x86") {
       abi_target = "i686-linux-androideabi"
     } else if (current_cpu == "arm64") {
-      # Place holder for arm64 support, not tested.
-      # TODO: Enable clang support for Android Arm64. http://crbug.com/539781
       abi_target = "aarch64-linux-android"
     } else if (current_cpu == "x64") {
       # Place holder for x64 support, not tested.
       # TODO: Enable clang support for Android x64. http://crbug.com/539781
       abi_target = "x86_64-linux-androideabi"
     } else if (current_cpu == "mipsel") {
       abi_target = "mipsel-linux-android"
     } else if (current_cpu == "mips64el") {
       # Place holder for mips64 support, not tested.
       abi_target = "mips64el-linux-androideabi"
@@ skipping 64 matching lines @@
   if (!is_clang) {
     libs += [ "atomic" ]
   }
 
   if (is_clang) {
     # Work around incompatibilities between bionic and clang headers.
     defines += [
       "__compiler_offsetof=__builtin_offsetof",
       "nan=__builtin_nan",
     ]
+
+    if (current_cpu == "x64" || current_cpu == "arm64" ||
+        current_cpu == "mips64el") {
+      # 64-bit targets build with NDK 21, 32-bit targets with NDK 16
+      # (see ./config.gni).  When using clang, NDK 21 defines snprintf to
+      # something for a kind of for of _FORTIFY_SOURCE support, see
+      # third_party/android_tools/ndk/platforms/android-21/arch-x86_64/usr/include/stdio.h
+      # Making snprintf a macro breaks base/strings/string_utils.h which
+      # defines base::snprintf().  So define snprintf to itself to force the
+      # NDK to not redefine it.  This disables _chk for snprintf, but since
+      # 32-bit versions use NDK 16 which doesn't have any fortify support, that
+      # seems ok.  b/32067310 tracks better fortify support with clang.
+      # TODO(thakis): Remove this once b/32067310 is fixed.
+      defines += [ "snprintf=snprintf" ]
+    }
   }
 
   # TODO(jdduke) Re-enable on mips after resolving linking
   # issues with libc++ (crbug.com/456380).
   if (current_cpu != "mipsel" && current_cpu != "mips64el") {
     ldflags += [ "-Wl,--warn-shared-textrel" ]
   }
 }
 
 config("executable_config") {
@@ skipping 35 matching lines @@
 
       # Avoid errors with current NDK:
       # "third_party/android_tools/ndk/toolchains/arm-linux-androideabi-4.6/prebuilt/linux-x86_64/bin/../lib/gcc/arm-linux-androideabi/4.6/include/arm_neon.h:3426:3: error: argument must be a constant"
       "-finstrument-functions-exclude-file-list=arm_neon.h",
     ]
   }
 }
 
 config("no_cygprofile_instrumentation") {
 }