No way to pass extra compile flags and defines

I need to pass defines to the compiler, but the arduino.json does not support such option. I tried putting a 
```
"defines":[...]
```
in the c_cpp_properties.json, but it is not picked up during compilation.
Same goes for extra compile flags. I tried putting
```
"compilerArgs": [...]
```
in the c_cpp_properties.json, but it is not picked up.
