Print errors from __gc finalizers instead of rethrowing them.

Finalizers are not supposed to throw errors -- this is undefined behavior.
Lua 5.1 - 5.3 and (previously) LuaJIT rethrow the error. This randomly
breaks some unrelated code that just happens to do an allocation. Bad.
Lua 5.4 catches the error and emits a warning instead. But warnings are
not enabled by default, so it fails silently. Even worse.
LuaJIT (now) catches the error and emits a VM event. The default event
handler function prints "ERROR in finalizer: ...".
Set a custom handler function with: jit.attach(handler, "errfin")

src/lj_vmevent.h

@@ -24,9 +24,10 @@
 /* VM event IDs. */
 typedef enum {
   VMEVENT_DEF(BC,	0x00003883),
-  VMEVENT_DEF(TRACE,	0xb2d91467),
-  VMEVENT_DEF(RECORD,	0x9284bf4f),
-  VMEVENT_DEF(TEXIT,	0xb29df2b0),
+  VMEVENT_DEF(TRACE,	0x12d91467),
+  VMEVENT_DEF(RECORD,	0x1284bf4f),
+  VMEVENT_DEF(TEXIT,	0x129df2b0),
+  VMEVENT_DEF(ERRFIN,	0x12d93888),
   LJ_VMEVENT__MAX
 } VMEvent;