perf tools: Fix 'make tools/perf'

Boris just raised another variant of building perf tools which is
broken:

 $ make tools/perf
 ...
     LINK /home/robert/cx/linux/tools/perf/perf
 gcc: error: ../linux/tools/lib/lk/liblk.a: No such file or directory

The variant wasn't considered by:

 107de372 perf tools: Fix build errors with O and DESTDIR make vars set

There are other variant of building perf too:

 $ make -C tools perf
 $ make -C tools/perf

Plus variants with O= and DESTDIR set.

This patch fixes the above and was tested with the following:

 $ make O=... DESTDIR=... tools/perf
 $ make O=... DESTDIR=... -C tools/ perf
 $ make O=... DESTDIR=... -C tools/perf
 $ make tools/perf
 $ make -C tools/ perf
 $ make -C tools/perf

Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Robert Richter <robert.richter@linaro.org>
Signed-off-by: Robert Richter <rric@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-tip-commits@vger.kernel.org
Link: http://lkml.kernel.org/r/20130716145036.GH8731@rric.localhost


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