tools lib traceevent: Define _GNU_SOURCE in Makefile

For the reasons stated on:

  commit 0a84f007
  Author: David Daney <david.daney@cavium.com>

    perf tools: Fix broken build by defining _GNU_SOURCE in Makefile
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: David Daney <david.daney@cavium.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/n/tip-e2nofbmj4uf0ykgsytxvt9pu@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/traceevent/Makefile

@@ -129,7 +129,7 @@ CFLAGS ?= -g -Wall
 
 # Append required CFLAGS
 override CFLAGS += $(CONFIG_FLAGS) $(INCLUDES) $(PLUGIN_DIR_SQ)
-override CFLAGS += $(udis86-flags)
+override CFLAGS += $(udis86-flags) -D_GNU_SOURCE
 
 ifeq ($(VERBOSE),1)
   Q =

tools/lib/traceevent/event-parse.c

@@ -24,7 +24,6 @@
  *  Frederic Weisbecker gave his permission to relicense the code to
  *  the Lesser General Public License.
  */
-#define _GNU_SOURCE
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>