perf tools: Add build test with GTK+

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 <[email protected]>
Cc: Ian Rogers <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Namhyung Kim <[email protected]>
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

tools/perf/tests/make

@@ -91,6 +91,7 @@ make_no_sdt	    := NO_SDT=1
 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
@@ -154,6 +155,7 @@ run += make_no_syscall_tbl
 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