Phobos in BetterC

[Vasyl Teliman via Digitalmars-d-learn]

I've tried to use Mallocator in BetterC but it seems it's not 
available there:

https://run.dlang.io/is/pp3HDq
This produces a linker error.

I'm wondering why Mallocator is not available in this mode (it 
would be intuitive to assume that it's working). Also I would 
like to know what parts of Phobos are available there (e.g. 
std.traits, std.typecons...).

Thanks in advance.