Command Line Order + Linker Errors

[dsimcha]

I'm running into some inexplicable linker errors when trying to 
compile a project.  I've tried two command lines to compile the 
project that I thought were equivalent except for the names of 
the output files:

// emptymain.d:
void main(){}

// test.d:
unittest {
     double[double] weights = [1:1.2, 4:2.3];
     import std.stdio;
     writeln("PASSED");
}

dmd -unittest emptymain.d test.d  // Linker errors

dmd -unittest test.d emptymain.d  // Works

Additionally, the linker errors only occur under a custom version 
of druntime.  Don't try to reproduce them under the stock 
version.  (For the curious, it's the precise heap scanning fork 
from https://github.com/rainers/druntime/tree/precise_gc2 .  I'm 
trying to get precise heap scanning ready for prime time.)

My real question, though, is why should the order of these files 
on the command line matter and does this suggest a compiler or 
linker bug?