perf test shell diff: Skip test if test_loop symbol is missing in the perf binary

The diff test depends on finding the symbol test_loop in perf and will
fail if perf has been stripped and no debug object is available. In that
case, skip the test instead.

Suggested-by: Adrian Hunter <[e-mail]>
Signed-off-by: Ian Rogers <[e-mail]>
Tested-by: Adrian Hunter <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/tests/shell/diff.sh

···
 perfdata2=$(mktemp /tmp/__perf_test.perf.data.XXXXX)
 perfdata3=$(mktemp /tmp/__perf_test.perf.data.XXXXX)
 testprog="perf test -w thloop"
+
+shelldir=$(dirname "$0")
+# shellcheck source=lib/perf_has_symbol.sh
+. "${shelldir}"/lib/perf_has_symbol.sh
+
 testsym="test_loop"
+
+skip_test_missing_symbol ${testsym}
 
 cleanup() {
   rm -rf "${perfdata1}"