dynamic linker flags with dub

[KytoDragon]

For anyone looking for a solution, i created a batch-file called 
"ldc2_random.bat" with this content:

```
@echo off
del myapp_*.pdb > NUL 2> NUL
ldc2 %* -L/PDB:myapp_%random%.pdb
```

and then set my compiler to "--compiler=ldc2_random.bat"