diff -up chromium-55.0.2883.75/third_party/boringssl/BUILD.gn.addrfix chromium-55.0.2883.75/third_party/boringssl/BUILD.gn
--- chromium-55.0.2883.75/third_party/boringssl/BUILD.gn.addrfix	2016-12-12 15:30:27.727834891 -0500
+++ chromium-55.0.2883.75/third_party/boringssl/BUILD.gn	2016-12-12 15:30:53.095709352 -0500
@@ -24,6 +24,7 @@ config("internal_config") {
     "BORINGSSL_IMPLEMENTATION",
     "BORINGSSL_NO_STATIC_INITIALIZER",
     "OPENSSL_SMALL",
+    "_POSIX_C_SOURCE=200112L",
   ]
   configs = [
     # TODO(davidben): Fix size_t truncations in BoringSSL.