perf build: Shellcheck support for OUTPUT directory

Migrate Makefile.tests to Build so that variables like rule_mkdir are
defined via Makefile.build (needed so the output directory can be
created). This requires SHELLCHECK being exported and the clean rule
tweaking to remove the files in find.

Change find "-perm -o=x" as it was failing on my Debian based Linux
kernel tree, switch to using "-executable".

Adding a filename prefix of "." to the shellcheck log files is a pain
and error prone in make, remove this prefix and just add the
shellcheck log files to .gitignore.

Fix the command echo so that running the test is displayed.

Fixes: 1638b11e ("perf tools: Add perf binary dependent rule for shellcheck log in Makefile.perf")
Reviewed-by: Athira Jajeev <atrajeev@linux.vnet.ibm.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20231129213428.2227448-1-irogers@google.com


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