Fix "undefined reference to '__atomic_is_lock_free'" errors on Linux

base/BUILD.gn

Index: base/BUILD.gn
diff --git a/base/BUILD.gn b/base/BUILD.gn
index a5f5d05201666aff9a87762ec06afbeffd1fc41e..ce8089159ad067f707944dd209ec98bd9426296d 100644
--- a/base/BUILD.gn
+++ b/base/BUILD.gn
@@ -20,6 +20,7 @@
 import("//build/buildflag_header.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/nacl/config.gni")
+import("//build/config/sysroot.gni")
 import("//build/config/ui.gni")
 import("//build/nocompile.gni")
 import("//testing/test.gni")
@@ -980,6 +981,11 @@ component("base") {
     ":debugging_flags",
   ]
 
+  # Needed for <atomic> if using newer C++ library than sysroot
+  if (!use_sysroot && (is_android || is_linux)) {
+    libs = [ "atomic" ]
+  }
+
   # Allow more direct string conversions on platforms with native utf8
   # strings
   if (is_mac || is_ios || is_chromeos) {