Add missing <functional> include am: 5b5fe9ef2d am: 0eafc4a437 am: 0a7b5b103f am: 5938e62dbf

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

Change-Id: I5075e7f300fba548a48bdfa6281a90bdc26bfaa2
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>