build: re-enable gdbjit, honor --gdb again

Note that you need to start node with --gdbjit for it to become effective.

configure

@@ -340,7 +340,7 @@ def configure_arm(o):
 
 
 def configure_node(o):
-  # TODO add gdb
+  o['variables']['v8_enable_gdbjit'] = 1 if options.gdb else 0
   o['variables']['v8_no_strict_aliasing'] = 1 # work around compiler bugs
   o['variables']['node_prefix'] = os.path.expanduser(options.prefix or '')
   o['variables']['node_install_npm'] = b(not options.without_npm)