-L only specifies the search path for libraries directly provided in the
link line with -l. Because -lopencsd isn't specified, it's only linked
because it's a dependency of -lopencsd_c_api. Dependencies like this are
resolved using the default system search paths or -rpath-link=... rather
than -L. This means that compilation only works if OpenCSD is installed
to the system rather than provided with the CSLIBS (-L) option.

This could be fixed by adding -Wl,-rpath-link=$(CSLIBS) but that is less
conventional than just adding -lopencsd to the link line so that it uses
-L. -lopencsd seems to have been removed in commit ed17b191
("perf tools: Drop requirement for libstdc++.so for libopencsd check")
because it was thought that there was a chance compilation would work
even if it didn't exist, but I think that only applies to libstdc++ so
there is no harm to add it back. libopencsd.so and libopencsd_c_api.so
would always exist together.

Testing
=======

The following scenarios now all work:

 * Cross build with OpenCSD installed
 * Cross build using CSLIBS=...
 * Native build with OpenCSD installed
 * Native build using CSLIBS=...
 * Static cross build with OpenCSD installed
 * Static cross build with CSLIBS=...

Committer testing:

  ⬢[acme@toolbox perf-tools]$ alias m
  alias m='make -k BUILD_BPF_SKEL=1 CORESIGHT=1 O=/tmp/build/perf-tools -C tools/perf install-bin && git status && perf test python ;  perf record -o /dev/null sleep 0.01 ; perf stat --null sleep 0.01'
  ⬢[acme@toolbox perf-tools]$ ldd ~/bin/perf | grep csd
  	libopencsd_c_api.so.1 => /lib64/libopencsd_c_api.so.1 (0x00007fd49c44e000)
  	libopencsd.so.1 => /lib64/libopencsd.so.1 (0x00007fd49bd56000)
  ⬢[acme@toolbox perf-tools]$ cat /etc/redhat-release
  Fedora release 36 (Thirty Six)
  ⬢[acme@toolbox perf-tools]$

Fixes: ed17b191 ("perf tools: Drop requirement for libstdc++.so for libopencsd check")
Reported-by: Radhey Shyam Pandey <radhey.shyam.pandey@amd.com>
Signed-off-by: James Clark <james.clark@arm.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Tested-by: Radhey Shyam Pandey <radhey.shyam.pandey@amd.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Uwe Kleine-König <uwe@kleine-koenig.org>
Cc: coresight@lists.linaro.org
Closes: https://lore.kernel.org/linux-arm-kernel/56905d7a-a91e-883a-b707-9d5f686ba5f1@arm.com/
Link: https://lore.kernel.org/all/36cc4dc6-bf4b-1093-1c0a-876e368af183@kleine-koenig.org/
Link: https://lore.kernel.org/r/20230707154546.456720-1-james.clark@arm.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>