The error variable breaks build on CentOS 6.7, due to collision with
global error symbol:

    CC       util/evlist.o
  cc1: warnings being treated as errors
  In file included from util/evlist.c:28:
  tools/include/linux/err.h: In function ‘ERR_PTR’:
  tools/include/linux/err.h:34: error: declaration of ‘error’ shadows a global declaration
  util/util.h:135: error: shadowed declaration is here

Using 'error_' name instead to fix it.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/n/tip-i9mdgdbrgauy3fe76s9rd125@git.kernel.org
Reported-by: Vinson Lee <vlee@twopensource.com>
[ Use 'error_' instead of 'err' to, visually, not diverge too much from include/linux/err.h ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Adding part of the kernel's <linux/err.h> interface:

  inline void * __must_check ERR_PTR(long error);
  inline long   __must_check PTR_ERR(__force const void *ptr);
  inline bool   __must_check IS_ERR(__force const void *ptr);

It will be used to propagate error through pointers in following
patches.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Reviewed-by: Raphael Beamonte <raphael.beamonte@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1441615087-13886-2-git-send-email-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>