Using D's precise GC when running an app with DUB

[Per Nordlöw]

How do I specify a druntime flag such as

     --DRT-gcopt=gc:precise

when running with dub as

     dub run --compiler=dmd --build=unittest

?

The precise GC flag was introduced in verison 2.085.0

See:
- https://dlang.org/changelog/2.085.0.html#gc_precise
- https://dlang.org/spec/garbage.html#precise_gc