Upgrade libopus to 8cf872a186b96085b1bb3a547afd598354ebeb87

This project was upgraded with external_updater.
Usage: tools/external_updater/updater.sh update libopus
For more info, check https://cs.android.com/android/platform/superproject/+/master:tools/external_updater/README.md

Test: TreeHugger
Change-Id: Ifb9d10d5a1ccb2e7c117b58494c05eb46835f0ad