[Bug plugins/62252] a callback to event PLUGIN_FINISH_TYPE segfaults

[klemen.jan.enova at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62252

--- Comment #2 from klemen.jan.enova at gmail dot com ---
TREE_CODE(type) returns an ERROR_MARK. So, (tree) event_data must not alias
with a tree. This plugin is from
https://github.com/gcc-mirror/gcc/blob/master/gcc/testsuite/g%2B%2B.dg/plugin/dumb_plugin.c.
There are no checks there, it just assumes it is a type represented as a tree.