gnu11 is the default now. am: f0096d9cd2 am: 4d91a48927

Original change: https://android-review.googlesource.com/c/platform/external/pthreadpool/+/2097114

Change-Id: Id82844d0689a97d404d58fd67c57d8c15e0dce81
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>