Use -std=gnu11, as in the upstream Makefile. am: 899c84ec81

Original change: https://android-review.googlesource.com/c/platform/external/libnl/+/3502791

Change-Id: I614dfb70b833f1914566a0a5abb7a635ec39b38d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>