Enable support for Linux audit subsystem using sys-process/audit

Packages describing “audit” as local USE flag

Package “audit” Flag Description
sys-apps/systemd Enable support for sys-process/audit
sys-apps/util-linux Use sys-process/audit to emit audit messages about system changes
sys-apps/policycoreutils Enable support for sys-process/audit and use the audit_* functions (like audit_getuid instead of getuid())

All packages providing a “audit” USE flag (16)