How to specify --arch option in dub.json

[mogu via Digitalmars-d-learn]

I use dub 1.2.1 to build my project. As convenience, I choose 
`dflags-windows-x86: ["-m32mscoff"]` option in dub.json of my 
library binding to specify default architecture in win32 
platform. But in the newest dub release, this cause a warning 
which told me to use DLFAGS environment or specify arch in 
command line. Is there any other ways to fix this for I don't 
want users of this library always build with a long command line 
args?