perf build: Fix traceevent plugins build race

perf build: Fix traceevent plugins build race

Ingo reported following build failure:

  $ make clean install
  ...
    CC       plugin_kmem.o
  fixdep: error opening depfile: ./.plugin_hrtimer.o.d: No such file or directory
  /home/mingo/tip/tools/build/Makefile.build:77: recipe for target
  'plugin_hrtimer.o' failed
  make[3]: *** [plugin_hrtimer.o] Error 2
  Makefile:189: recipe for target 'plugin_hrtimer-in.o' failed
  make[2]: *** [plugin_hrtimer-in.o] Error 2
  Makefile.perf:414: recipe for target 'libtraceevent_plugins' failed
  make[1]: *** [libtraceevent_plugins] Error 2
  make[1]: *** Waiting for unfinished jobs....

Currently we have the install-traceevent-plugins target being dependent
on $(LIBTRACEEVENT), which will actualy not build any plugin. So the
install-traceevent-plugins target itself will try to build plugins,
but..

Plugins built is also triggered by perf build itself via
libtraceevent_plugins target.

This might cause a race having one make thread removing temp files from
another and result in above error. Fixing this by having proper plugins
build dependency before installing plugins.

Reported-and-Tested-by:: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1448546044-28973-3-git-send-email-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>