libobs/UI: Allow Access To argc/argv

This paves the way for plugins to have access to the argc/argv used
when spawning OBS. Notably, this will allow a patch to obs-browser that
passes through command line arguments on macOS to CEF.

libobs/obs.h

@@ -239,6 +239,12 @@ struct obs_source_frame {
 	bool                prev_frame;
 };
 
+/** Access to the argc/argv used to start OBS. What you see is what you get. */
+struct obs_cmdline_args {
+	int argc;
+	char **argv;
+};
+
 /* ------------------------------------------------------------------------- */
 /* OBS context */
 
@@ -291,6 +297,24 @@ EXPORT uint32_t obs_get_version(void);
 /** @return The current core version string */
 EXPORT const char *obs_get_version_string(void);
 
+/**
+ * Sets things up for calls to obs_get_cmdline_args. Called onl yonce at startup
+ * and safely copies argv/argc from main(). Subsequent calls do nothing.
+ *
+ * @param  argc  The count of command line arguments, from main()
+ * @param  argv  An array of command line arguments, copied from main() and ends
+ *               with NULL.
+ */
+EXPORT void obs_set_cmdline_args(int argc, char **argv);
+
+/**
+ * Get the argc/argv used to start OBS
+ *
+ * @return  The command line arguments used for main(). Don't modify this or
+ *          you'll mess things up for other callers.
+ */
+EXPORT struct obs_cmdline_args obs_get_cmdline_args(void);
+
 /**
  * Sets a new locale to use for modules.  This will call obs_module_set_locale
  * for each module with the new locale.