Linker cannot find malloc and free on OS X

[Nordlöw via Digitalmars-d-learn]

My gmp-d tests successfully on Linux as

dub test

but on OS X it fails as

Undefined symbols for architecture x86_64:
   "free", referenced from:
   ...
   "malloc", referenced from:
   ...

Any ideas on why?

https://github.com/nordlow/gmp-d/issues/4#issuecomment-305974761