They were used in two-phase sycalls entry tracing, but this functionality
was then moved to the arch/x86/entry/common.c:syscall_trace_enter() function,
in the following commit:
1f484aa69046 ("x86/entry: Move C entry and exit code to arch/x86/entry/common.c")
syscall_trace_enter() now uses the defines from <linux/audit.h>,
so these defines entry_64.S are no longer used anywhere.