tools lib traceevent: Do not generate dependency for system header files

tools lib traceevent: Do not generate dependency for system header files

Ingo reported (again!) that 'make clean' on perf/traceevent does not
work due to some reason with system header file. Quotes Ingo:

 "Note that the old dependency related build failure thought to be
  fixed in commit 860df5833e46 is back:

   make[1]: *** No rule to make target
   `/usr/lib/gcc/x86_64-redhat-linux/4.7.0/include/stddef.h', needed by `.trace-seq.d'.  Stop.

  'make clean' itself does not work in libtraceevent:

   comet:~/tip/tools/lib/traceevent> make clean
   make: *** No rule to make target `/usr/lib/gcc/x86_64-redhat-linux/4.7.0/include/stddef.h', needed by `.trace-seq.d'.  Stop.

  So I had to clean it out manually:

   comet:~/tip/tools/lib/traceevent> git ls-files --others | xargs rm
   comet:~/tip/tools/lib/traceevent>

  and then things build fine."

Try to fix it by excluding system headers from dependency generation.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Reported-by: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@amd64.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/1351241752-2919-1-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>