perf lib: Introduce rtrim

Remove the trailing whitespaces.

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-8bxozh5lyixgjmziqaxo9675@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/util.h

@@ -264,4 +264,6 @@ bool is_power_of_2(unsigned long n)
 
 size_t hex_width(u64 v);
 
+char *rtrim(char *s);
+
 #endif