Sets the message levels which are always fatal, in any log domain.
When a message with any of these levels is logged the program terminates. You can only set the levels defined by GLib to be fatal. g_log_level_error is always fatal.
You can also make some message levels fatal at runtime by setting the `G_DEBUG` environment variable (see [Running GLib Applications]( glib-running.html)).
Libraries should not call this function, as it affects all messages logged by a process, including those from other libraries.
Structured log messages (using log_structured and log_structured_array) are fatal only if the default log writer is used; otherwise it is up to the writer function to determine which log messages are fatal. See Using Structured Logging.
the mask containing bits set for each level of error which is to be fatal
the old fatal mask