perf jvmti: Link against tools/lib/string.o to have weak strlcpy()

perf jvmti: Link against tools/lib/string.o to have weak strlcpy()

That is needed in systems such some S/390 distros.

  $ readelf -s /tmp/build/perf/jvmti/jvmti-in.o | grep strlcpy
	452: 0000000000002990   125 FUNC    WEAK   DEFAULT  119 strlcpy
  $

Thanks to Jiri Olsa for fixing up my initial stab at this, I forgot how
Makefiles are picky about spaces versus tabs.

Reported-by: Thomas Richter <tmricht@linux.ibm.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andreas Krebbel <krebbel@linux.ibm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Sergey Melnikov <melnikov.sergey.v@gmail.com>
Link: https://lkml.kernel.org/n/tip-x8vg9sffgb2t1tzqmhkrulh7@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>