perf tools: Move get_current_dir_name() cond prototype out of util.h

And in a separate header, so that we erode util.h a bit more.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-xpzvuu9d0gei9jl9bkzgobln@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>