The GCC compiler flags that control unused warnings include:
-Wunused-function -Wunused-label -Wunused-parameter -Wunused-value -Wunused-variable -Wunused(=all of the above)
Each of these has a corresponding negative form with "no-" inserted after the W which turns off the warning (in case it was turned on by -Wall, for example). Thus, in your case you should use
Of course this works for the whole code, not just compile-time asserts. For function-specific behaviour, have a look at Function attributes.