Support of -run and source code from stdin

[Andre Pany]

Hi,
Dmd and ldc supports running source code from stdin:

```
echo 'void main(){}' | dmd -run -
```

It seems GDC does not support argument -run and I do not know 
wheter it supports reading source code from stdin?

Could this 2 featured be added to gdc?
This would solve the probe file issue mentioned here 
https://forum.dlang.org/post/uwxndbpxspwaofolksbr@forum.dlang.org

Kind regards
Andre