[avr-gcc-list] How to suppres trigraph warning messages?

[Bob Paddock]

I have a string:

char date[] = "??/??/??";

to which I receive:

main.c:352:94: trigraph ??/ ignored, use -trigraphs to enable

I have tried adding "-trigraphs" to the CFLAGS then escaping
the trigraph:

char date[] = "\??/\??/??";

but that still tells me to enable the trigraphs.

I do not want trigraphs, how do I make the warning go away?
Local policy says there can be no warnings in compiles.

FYI:
"??/" becomes a "\" if you really want trigraphs (who does?).