Add missing <functional> include am: 5b5fe9ef2d am: 0eafc4a437 am: 0a7b5b103f

Original change: https://android-review.googlesource.com/c/platform/external/libldac/+/2759541

Change-Id: I5189e73a4bc4be46b2e9afcc74070edcc9da62bf
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>