Revert "build: switch debug mode from -O0 to -Og"
Revert "build: switch debug mode from -O0 to -Og"

This reverts commit e988521b89d95bbe0c51feaadb9706522351d0aa. It triggers a bug
int gcc variable tracking, and there are reports it significantly slows down
compilation.

scylladb/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla