test_build_options.py: exempt AP_AIRSPEED_NMEA_ENABLED from testing

cpp file makes this only exist for Rover/Sub

Tools/autotest/test_build_options.py

@@ -241,6 +241,9 @@ def assert_feature_in_code(self, defines, feature):
                     'HAL_PERIPH_SUPPORT_LONG_CAN_PRINTF',  # no symbol
                     'AP_DRONECAN_VOLZ_FEEDBACK_ENABLED',  # broken, no subscriber
                 ])
+                if target.lower() not in frozenset(["rover", "sub"]):
+                    # only Rover and Sub get nmea airspeed
+                    set.add('AP_AIRSPEED_NMEA_ENABLED')
                 if define not in compiled_in_feature_defines:
                     error = f"feature gated by {define} not compiled into ({target}); extract_features.py bug?"
                     if define in feature_define_whitelist: