tools build: Don't set libunwind as available if test-all.c build succeeds

The tools/build/feature/test-all.c file tries to detect the expected,
most common set of libraries/features we expect to have available to
build perf with.

At some point libunwind was deemed not to be part of that set of
libries, but the patches making it to be opt-in ended up forgetting some
details, fix one more.

Testing it:

  $ rm -rf /tmp/build/$(basename $PWD)/ ; mkdir -p /tmp/build/$(basename $PWD)/
  $ rpm -q libunwind-devel
  libunwind-devel-1.8.0-3.fc40.x86_64
  $ make -k LIBUNWIND=1 CORESIGHT=1 O=/tmp/build/$(basename $PWD)/ -C tools/perf install-bin |& grep unwind && ldd ~/bin/perf | grep unwind
  ...                               libunwind: [ on  ]
    CC      /tmp/build/perf-tools-next/arch/x86/tests/dwarf-unwind.o
    CC      /tmp/build/perf-tools-next/arch/x86/util/unwind-libunwind.o
    CC      /tmp/build/perf-tools-next/util/arm64-frame-pointer-unwind-support.o
    CC      /tmp/build/perf-tools-next/tests/dwarf-unwind.o
    CC      /tmp/build/perf-tools-next/util/unwind-libunwind-local.o
    CC      /tmp/build/perf-tools-next/util/unwind-libunwind.o
	  libunwind-x86_64.so.8 => /lib64/libunwind-x86_64.so.8 (0x00007f615a549000)
	  libunwind.so.8 => /lib64/libunwind.so.8 (0x00007f615a52f000)
  $ sudo rpm -e libunwind-devel
  $ rm -rf /tmp/build/$(basename $PWD)/ ; mkdir -p /tmp/build/$(basename $PWD)/
  $ make -k LIBUNWIND=1 CORESIGHT=1 O=/tmp/build/$(basename $PWD)/ -C tools/perf install-bin |& grep unwind && ldd ~/bin/perf | grep unwind
  Makefile.config:653: No libunwind found. Please install libunwind-dev[el] >= 1.1 and/or set LIBUNWIND_DIR
  ...                               libunwind: [ OFF ]
    CC      /tmp/build/perf-tools-next/arch/x86/tests/dwarf-unwind.o
    CC      /tmp/build/perf-tools-next/arch/x86/util/unwind-libdw.o
    CC      /tmp/build/perf-tools-next/util/arm64-frame-pointer-unwind-support.o
    CC      /tmp/build/perf-tools-next/tests/dwarf-unwind.o
    CC      /tmp/build/perf-tools-next/util/unwind-libdw.o
  $

Should be in a separate patch, but tired now, so also adding a message
about the need to use LIBUNWIND=1 in the output when its not available,
so done here as well.

So, now when the devel files are not available we get:

  $ make -k LIBUNWIND=1 CORESIGHT=1 O=/tmp/build/$(basename $PWD)/ -C tools/perf install-bin |& grep unwind && ldd ~/bin/perf | grep unwind
  Makefile.config:653: No libunwind found. Please install libunwind-dev[el] >= 1.1 and/or set LIBUNWIND_DIR and set LIBUNWIND=1 in the make command line as it is opt-in now
  ...                               libunwind: [ OFF ]
  $

Fixes: 13e17c9f ("perf build: Make libunwind opt-in rather than opt-out")
Reported-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Ingo Molnar <mingo@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Dmitriy Vyukov <dvyukov@google.com>
Cc: Ian Rogers <irogers@google.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/Z_AnsW9oJzFbhIFC@x1


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