tracing/events: fix the include file dependencies

The TRACE_EVENT depends on the include/linux/tracepoint.h first
and include/trace/ftrace.h later, if we include the ftrace.h early,
a building error will occur.

Both define TRACE_EVENT in trace_a.h and trace_b.h, if we include
those in .c file, like this:

#define CREATE_TRACE_POINTS
include <trace/events/trace_a.h>
include <trace/events/trace_b.h>

The above will not work, because the TRACE_EVENT was re-defined by
the previous .h file.
Reported-by: Wei Yongjun <yjwei@cn.fujitsu.com>
Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
LKML-Reference: <4A937F5E.3020802@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

include/linux/tracepoint.h

@@ -180,6 +180,7 @@ static inline void tracepoint_synchronize_unregister(void)
 }
 
 #define PARAMS(args...) args
+#endif
 
 #ifndef TRACE_EVENT
 /*
@@ -287,5 +288,3 @@ static inline void tracepoint_synchronize_unregister(void)
 #define TRACE_EVENT(name, proto, args, struct, assign, print)	\
 	DECLARE_TRACE(name, PARAMS(proto), PARAMS(args))
 #endif
-
-#endif

include/trace/define_trace.h

@@ -56,6 +56,7 @@
 #include <trace/ftrace.h>
 #endif
 
+#undef TRACE_EVENT
 #undef TRACE_HEADER_MULTI_READ
 
 /* Only undef what we defined in this file */