perf test: Support external tests for separate objdir

Extend the searching for the test files so that it works when running
perf from a separate objdir, and also when the perf executable is
symlinked.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20240813213651.1057362-2-ak@linux.intel.com


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