freebsd_wlan: Fix compilation of ieee80211_ioctl.h under GCC2 in C mode.

GCC2 tolerates [] FLAs in C++ mode but not in C mode, as discovered
when trying to build wpa_supplicant against R1/beta4. A workaround
was added there for now, but this is the more general solution.

src/libs/compat/freebsd_wlan/net80211/ieee80211_ioctl.h

@@ -785,7 +785,11 @@ struct ieee80211_haiku_join_req {
 	uint32 i_key_mode;
 
 	uint32 i_key_len;
+#if __GNUC__ == 2
+	uint8 i_key[0];
+#else
 	uint8 i_key[];
+#endif
 };
 #endif /* __HAIKU__ */