Just stick assert.h in there and don't worry about it.
Then in the README/INSTALL note that
if users run into trouble (failing tests), they should run perl Makefile.PL DEFINE=-DNDEBUG=0
and test again (with TEST_VERBOSE=1).
That should trigger assert.h to spit out extra stuff.
You could also do some creative stuff to make this happen automatically but why bother ?:)
MJDsays "you can't just make shit up and expect the computer to know what you mean, retardo!"