[Tools] Add useconfig option for scons.

tools/building.py

@@ -285,6 +285,16 @@ def PrepareBuilding(env, root_directory, has_libcpu=False, remove_components = [
             menuconfig(Rtt_Root)
             exit(0)
 
+    AddOption('--useconfig',
+                dest = 'useconfig',
+                type='string',
+                help = 'make rtconfig.h from config file.')
+    configfn = GetOption('useconfig')
+    if configfn:
+        from menuconfig import mk_rtconfig
+        mk_rtconfig(configfn)
+        exit(0)
+
     # add comstr option
     AddOption('--verbose',
                 dest='verbose',