Separate "generated" dir, fixing dustmite build on OSX

[Abscissa]

Adjusted the makefiles to put generated files into their own separate "generated" directory, much like phobos's posix makefile.

Aside from cleanliness, this is needed to avoid an OSX build problem with dustmite: OSX is case-insensitive so the "dustmite" build target conflicted with the "DustMite" directory.

[MartinNowak]

Can we adopt the MODEL:=default behavior from druntime and phobos.

MODEL:=default
ifneq (default,$(MODEL))
      MODEL_FLAG:=-m$(MODEL)
endif

[Abscissa]

Probably a good idea, but I wasn't immediately sure how to do that (in the other repos it seemed to involve automatic re-invoking of make) and the really important thing was to get the executables out of the repo's base directory. I'm sure what you suggest would be worth someone making a pull request, though.

EDIT: Oh, I didn't read that right and thought you meant "debug vs release". What I put in there for MODEL was actually copy-pasted from one of the other repos (dmd's repo, IIRC). But in any case, yea, that may be a good idea and worth someone putting together a pull req for it.

[MartinNowak]

The point here is to avoid any default architecture in the makefile and use whatever the compiler default is.
This is how we solved it for druntime and phobos and I think it makes sense here too.

[Abscissa]

On Thu, 15 Aug 2013 13:49:37 -0700
Martin Nowak notifications@github.com wrote:

The point here is to avoid any default architecture in the makefile
and use whatever the compiler default is. This is how we solved it
for druntime and phobos and I think it makes sense here too.

Right. I have no arguments against that.