Fix typo in libc++abi

third_party/libc++abi/BUILD.gn

 # Copyright 2015 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.
 
 source_set("libc++abi") {
   visibility = [ "//buildtools/third_party/libc++" ]
   sources = [
     "trunk/src/abort_message.cpp",
     "trunk/src/cxa_aux_runtime.cpp",
     "trunk/src/cxa_default_handlers.cpp",
@@ skipping 10 matching lines @@
     "trunk/src/cxa_unexpected.cpp",
     "trunk/src/cxa_vector.cpp",
     "trunk/src/cxa_virtual.cpp",
     "trunk/src/fallback_malloc.cpp",
     "trunk/src/private_typeinfo.cpp",
     "trunk/src/stdlib_exception.cpp",
     "trunk/src/stdlib_new_delete.cpp",
     "trunk/src/stdlib_stdexcept.cpp",
     "trunk/src/stdlib_typeinfo.cpp",
   ]
-  if (is_linux && !is_mac) {
-    sources == [ "trunk/src/cxa_thread_atexit.cpp" ]
+  if (is_posix && !is_mac) {
+    sources += [ "trunk/src/cxa_thread_atexit.cpp" ]
   }
   configs -= [
     "//build/config/compiler:chromium_code",
     "//build/config/compiler:no_rtti",
     "//build/config/gcc:no_exceptions",
   ]
   configs += [
     "//build/config/compiler:no_chromium_code",
     "//build/config/compiler:rtti",
     "//buildtools/third_party/libc++:config",
   ]
 }