How to stop DMD from exploding the executable file size?

[ryuukk_]

Thanks to @Herringway on IRC, he made me check dmd/ldc linker 
invocation and check the difference


LDC seem to add:

```
     /OPT:REF
     /OPT:ICF
```

Adding both and now DMD produce small file! (1mb vs 10mb before)

Can we have them enabled by default?