Support cpp backend for libfmq am: 4d606ccb65 am: 7888a5c05a

Original change: https://android-review.googlesource.com/c/platform/system/libfmq/+/3364942

Change-Id: Ic3dc7c72d6bce653fe94a43142b7f78f8f9b8138
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>