error: Implement the warn and free Error functions

Implement warn_report_err() and warn_reportf_err() functions which
are the same as the error_report_err() and error_reportf_err()
functions except report a warning instead of an error.

Signed-off-by: Alistair Francis <alistair.francis@xilinx.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <276ff93eadc0b01b8243cc61ffc331f77922c0d0.1499866456.git.alistair.francis@xilinx.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
diff --git a/include/qapi/error.h b/include/qapi/error.h
index 7e532d0..af53b34 100644
--- a/include/qapi/error.h
+++ b/include/qapi/error.h
@@ -267,11 +267,22 @@
 void error_free_or_abort(Error **errp);
 
 /*
+ * Convenience function to warn_report() and free @err.
+ */
+void warn_report_err(Error *err);
+
+/*
  * Convenience function to error_report() and free @err.
  */
 void error_report_err(Error *err);
 
 /*
+ * Convenience function to error_prepend(), warn_report() and free @err.
+ */
+void warn_reportf_err(Error *err, const char *fmt, ...)
+    GCC_FMT_ATTR(2, 3);
+
+/*
  * Convenience function to error_prepend(), error_report() and free @err.
  */
 void error_reportf_err(Error *err, const char *fmt, ...)