perf tools: Fix build error with bison 2.6

Bison 2.6 started to generate parse_events_parse() declaration in header. In
this case we have redundant redeclaration:

util/parse-events.c:29:5: error: redundant redeclaration of ‘parse_events_parse’ [-Werror=redundant-decls]
In file included from util/parse-events.c:14:0:
util/parse-events-bison.h:99:5: note: previous declaration of ‘parse_events_parse’ was here
cc1: all warnings being treated as errors

Let's disable -Wredundant-decls for util/parse-events.c since it includes
header we can't control.

Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20120723210407.GA25186@shutemov.name
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>