[dmd-internals] DMD bootstrapping version requirements

[Walter Bright via dmd-internals]

On 2/16/2017 7:43 PM, Daniel Murphy wrote:
> Why exactly do you need that switch to convert the backend?  As long
> as the source files are passed on the command line and have a module
> declaration then they don't care which directory they are in.

I want to use separate compilation for the back end, rather than lumping it into 
one big compile. One reason is asserts cannot be turned off for the back end. 
(They are for the front end for compilation speed reasons.)

Incremental compile times become excessive, because everything has to be recompiled.

Tracking down a compiler bug can get hard when one cannot use separate 
compilation. It's a bitch tracking them down in Phobos, but at least I can cut 
things down to size with separate compilation. I just did that for 
https://github.com/dlang/dmd/pull/6546, and I'm not so sure I could have found 
it without separate compilation - it certainly would have taken much, much longer.