Don't blame diagnostics; it doesn't add any warnings, it just explains them. I hope you are turning on warnings in your code even when not doing the -c thing. With a suitably non-decrepit version of perl, put a use warnings; no warnings "syntax"; at the top of your code, or switch to a non-GNU coding style, with no space between function name and left parenthesis.

I know this warning is somewhat controversial, because it in effect is prejudiced against a common coding style, but for those of us who don't use that coding style and do call builtins and subs without (), it can be a lifesaver.