[dmd-internals] pull requ. 6068 (issue 15257) -- need advice

[Cauterite via dmd-internals]

I've been working on this patch:
https://github.com/dlang/dmd/pull/6068
which fixes up some severe flaws in the inline assembler. But 
I've hit a roadblock.

The patch is almost correct, everything *appears* to be working 
as intended, except for this obscure bug that has somehow been 
introduced as a side effect of the patch:

     Makefile:205: recipe for target 'test_results/d_do_test.exe' 
failed
     gmake: *** [test_results/d_do_test.exe] Error 127

See my latest comment for details: 
https://github.com/dlang/dmd/pull/6068#issuecomment-242147910

The problem is, I don't know where to start with debugging this. 
I'm really struggling to envision how my patch could've caused 
it. Even some basic suggestions or speculation would be much 
appreciated.

This is my first time working on the DMD codebase, so I've been 
discovering the details of its componentry along the way as I 
diagnosed the bugs I encountered. Because this bug is manifesting 
outside the compiler, I can't think of how I can trace it back to 
its source.

Thanks for any help you can provide. I've been working hard on 
this patch, so I really want to see it completed.