portduino, handle sdl2 builds (#8355)

fix linux native build by adding sdl2 libraries

variants/native/portduino/platformio.ini

@@ -17,6 +17,7 @@ extends = native_base
 build_flags = ${native_base.build_flags}
   !pkg-config --libs libulfius --silence-errors || :
   !pkg-config --libs openssl --silence-errors || :
+  !pkg-config --cflags --libs sdl2 --silence-errors || :
 
 [env:native-tft]
 extends = native_base