Each numbered warning message has a default number indicating a level of importance. This number is specified in the MDF and ranges from -9 to 9. The higher the number, the more important the warning.
Warning messages can be disabled by adjusting the warning level threshold
using the -mwarn driver option, (see Warn Option). Any warnings whose level is below
that of the current threshold are not displayed. Warnings from the Clang front end (C99)
cannot be disabled.
The default threshold is 0 which implies that only warnings with a warning level of 0 or higher will be displayed by default. The information in this option is propagated to all compiler applications, so its effect will be observed during all stages of the compilation process.
All warnings can be disabled using the -w option.