GC assertions should print out more information
When a gc assertion fails, we just get a message that an assertion failed on line n.
It would be really nice if the messages had more information about why the assertion failed. For example, there's an assertion that the rehash threshold is valid. When it fails, we just get a line number. If the message also included the value of the rehash threshold, we'd have more information during the failure about what happened. Without this, we have to run gdb and put a breakpoint there or add some prints and rebuild cmucl. Neither of these is really appealing.