So that when we use:
make -C tools/perf build-test
One of the entries will ask for building with GTK+ 2.
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
 make_no_syscall_tbl := NO_SYSCALL_TABLE=1
 make_with_clangllvm := LIBCLANGLLVM=1
 make_with_libpfm4   := LIBPFM4=1
+make_with_gtk2      := GTK2=1
 make_tags           := tags
 make_cscope         := cscope
 make_help           := help
 run += make_with_babeltrace
 run += make_with_clangllvm
 run += make_with_libpfm4
+run += make_with_gtk2
 run += make_help
 run += make_doc
 run += make_perf_o