perf tools: Move conditional O_CLOEXEC to util.h

To be more generally available and get the build on centos:5 to
work after we use O_CLOEXEC in the next patch, in the util/dso.c file.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Cc: Wang YanQing <udknight@gmail.com>
Link: https://lkml.kernel.org/n/tip-vsjbiydh15pfqomxw1kx64ex@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>