Debug info for druntime.

[ciechowoj]

What is the fastest way to have the detailed debug info for 
druntime? I have a program that fails in Fiber constructor after 
I create and delete at least 68_209 Fibers one after another. For 
68_208 works fine, one more and it aborts. I'm trying to use gdb 
to debug, but most likely don't have symbols for druntime. I 
compiled the druntime from source, is there a way to make the 
dmd/dub use the source compiled version?