base: remove -latomic in CrOS chroot

base/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.
 
 # HOW TO WRITE CONDITIONALS IN THIS FILE
 # ======================================
 #
 # In many other places, one would write a conditional that expresses all the
 # cases when a source file is used or unused, and then either add or subtract
 # it from the sources list in that case
@@ skipping 1111 matching lines @@
   ]
 
   public_deps = [
     ":base_static",
     ":build_date",
     ":debugging_flags",
   ]
 
   # Needed for <atomic> if using newer C++ library than sysroot
   if (!use_sysroot && (is_android || (is_linux && !is_chromecast))) {
-    libs = [ "atomic" ]
+    # libatomic is not provided by the CrOS sysroot, so don't attempt
+    # to link to it under these circumstances. is_chromeos = true /
+    # target_os = "chrome_os" are not exclusive to the CrOS sysroot
+    # (since these can be built for desktop Linux too), so check the
+    # toolchain to make sure.
+    if (host_toolchain != "//build/toolchain/cros:host") {

[Dirk Pranke, 2017/04/25 19:18:06]

I'd fold the comment and the check into the outer if condition. Having an if
contain a single additional if reads a little weird.

Otherwise lgtm.

+      libs = [ "atomic" ]
+    }
   }
 
   if (use_experimental_allocator_shim) {
     # TODO(primiano): support other platforms, currently this works only on
     # Linux/CrOS/Android. http://crbug.com/550886 .
     sources += [
       "allocator/allocator_shim.cc",
       "allocator/allocator_shim.h",
       "allocator/allocator_shim_internals.h",
       "allocator/allocator_shim_override_cpp_symbols.h",
@@ skipping 1549 matching lines @@
 }
 
 fuzzer_test("base_json_correctness_fuzzer") {
   sources = [
     "json/correctness_fuzzer.cc",
   ]
   deps = [
     ":base",
   ]
 }