sdk: be C++ friendly

This renames the weston_surface's private member to configure_private
and externs "C" the headers of the SDK.
diff --git a/shared/config-parser.h b/shared/config-parser.h
index 314057a..1d0ee3f 100644
--- a/shared/config-parser.h
+++ b/shared/config-parser.h
@@ -23,6 +23,10 @@
 #ifndef CONFIGPARSER_H
 #define CONFIGPARSER_H
 
+#ifdef  __cplusplus
+extern "C" {
+#endif
+
 enum config_key_type {
 	CONFIG_KEY_INTEGER,		/* typeof data = int */
 	CONFIG_KEY_UNSIGNED_INTEGER,	/* typeof data = unsigned int */
@@ -69,5 +73,9 @@
 parse_options(const struct weston_option *options,
 	      int count, int *argc, char *argv[]);
 
+#ifdef  __cplusplus
+}
+#endif
+
 #endif /* CONFIGPARSER_H */