From the gcc manual:
Many options have long names starting with -f or with -W---for example,
-fforce-mem, -fstrength-reduce, -Wformat and so on. Most of these have
both positive and negative forms; the negative form of -ffoo would be
-fno-foo. This manual documents only one of these two forms, whichever
one is not the default.
But if you're asking whether there is a source-level warning disable, I'm not aware if that feature exists in gcc.
