m_config: support flatten and merge flags for suboptions

M_OPT_PREFIXED allows adding top-level options with the suboption
mechanism. The point of this is that, even though these options are
top-level options, they don't need to be added directly to a top-
level option array (such as mplayer_opts[]). Instead, the suboption
can be defined in a separate source file. Only a suboption declaration
is needed to add these options.

M_OPT_MERGE is similar to M_OPT_PREFIXED, but doesn't add the name of
the suboptions entry as prefix.

Given you have a suboption declaration "prefix" and the suboption
"subopt", you can pass them as follows on the command line:
  normal:           --prefix=subopt=value
  M_OPT_PREFIXED:   --prefix-subopt=value
  M_OPT_MERGE:      --subopt=value

1 files changed, 2 insertions, 0 deletions

diff --git a/m_config.h b/m_config.h
index 10f0cb67ed..beeab80a53 100644
--- a/m_config.h
+++ b/m_config.h
@@ -42,6 +42,8 @@ struct m_config_option {
     void *global_backup;
     // See \ref ConfigOptionFlags.
     unsigned int flags;
+    // If this is a suboption, the option that contains this option.
+    struct m_config_option *parent;
 };
 
 // Profiles allow to predefine some sets of options that can then