tracing: add global-clock option to provide cross CPU clock to traces

Impact: feature to allow better serialized clock

This patch adds an option called "global-clock" that will allow
the tracer to switch to a slower but more accurate (across CPUs)
clock.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>

kernel/trace/trace.h

@@ -667,6 +667,7 @@ enum trace_iterator_flags {
 	TRACE_ITER_PRINTK_MSGONLY	= 0x10000,
 	TRACE_ITER_CONTEXT_INFO		= 0x20000, /* Print pid/cpu/time */
 	TRACE_ITER_LATENCY_FMT		= 0x40000,
+	TRACE_ITER_GLOBAL_CLK		= 0x80000,
 };
 
 /*