util: rename list_empty() to list_is_empty()

This makes it clear that it's a boolean test and not an action
(eg. "empty the list").

Reviewed-by: Eric Engestrom <eric@engestrom.ch>

src/compiler/nir/nir_validate.c

@@ -498,7 +498,7 @@ validate_deref_instr(nir_deref_instr *instr, validate_state *state)
     * conditions expect well-formed Booleans.  If you want to compare with
     * NULL, an explicit comparison operation should be used.
     */
-   validate_assert(state, list_empty(&instr->dest.ssa.if_uses));
+   validate_assert(state, list_is_empty(&instr->dest.ssa.if_uses));
 
    /* Only certain modes can be used as sources for phi instructions. */
    nir_foreach_use(use, &instr->dest.ssa) {