tools: start on callgraph example using columnview

This just serves as a prototyping ground so that we can have a callgraph
view widget in the future based on these principles. It also shows some
areas that still need work, such as sorting within the tree and fixing the
text offset calculation for ELF symbols.

src/tools/meson.build

@@ -56,3 +56,12 @@ if get_option('agent')
          install: true,
   )
 endif
+
+if get_option('gtk')
+  callgraph = executable('callgraph', ['callgraph.c'],
+    dependencies: [libsysprof_analyze_static_dep,
+                   dependency('gtk4', version: gtk_req_version)],
+          c_args: tools_cflags,
+         install: false,
+  )
+endif