Snippets for openvswitch 4.0.0 from Alpine armv7

Sourced from https://build.alpinelinux.org/buildlogs/build-edge-armv7/community/openvswitch/openvswitch-4.0.0-r0.log.

• lib/backtrace.c:113:1: warning: 'read_received_backtrace' defined but not used [-Wunused-function]
    113 | read_received_backtrace(int fd OVS_UNUSED, void *dest OVS_UNUSED,
        | ^~~~~~~~~~~~~~~~~~~~~~~