Actually, I grep'd for it in both 5.8 and 5.6.1 sources before I answered. No hits. It seems the reason for that is that the define in question is PERL_DESTRUCT_LEVEL rather than PERL_DESTRUCTOR_LEVEL. I should have been a little more general with my grep the first time, I suppose.

-sauoq
"My two cents aren't worth a dime.";