What is the equivalent of -version=Flag for conditional compilation in the ldc2 compiler?

[data pulverizer via Digitalmars-d-learn]

Hi,

I was switching from dmd to ldc2 and would like to know the 
equivalent command line for conditional compilation -version=Flag 
I was using in dmd. I checked the ldc2 --help but didn't see 
anything relevant. Version there refers to compiler version or 
some other unrelated things.

Thanks