PKG_CHECK_MODULES syntax error near unexpected token 'DEPS,'

The next time you bash your brains against autotools for a while wondering why your perfectly good PKG_CHECK_MODULES() macro, as cut and paste directly from the recommended configure.ac entry for the package you're trying to integrate (in this case libmemcached), and you get the error message PKG_CHECK_MODULES syntax error near unexpected token 'DEPS,' on one system and not on another, it's probably because you're missing the pkg-config package on the failing system.

It would be nice if the error message gave you a clue, but it doesn't and probably can't, because the macro simply doesn't exist until the package is installed. So I'm telling you. Go forth and code now that that irritation is gone.