perf build: Add fixdep to .gitignore

perf build: Add fixdep to .gitignore

Commit 7c422f5572667fef0db38d2046ecce69dcf0afc8 ("tools build: Build
fixdep helper from perf and basic libs") dynamically creates fixdep
during the perf building. Add it to .gitignore.

Signed-off-by: Yunlong Song <yunlong.song@huawei.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Wang Nan <wangnan0@huawei.com>
Fixes: 7c422f557266 ("tools build: Build fixdep helper from perf and basic libs")
Link: http://lkml.kernel.org/r/1444899116-8220-1-git-send-email-yunlong.song@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>