[D-runtime] druntime and 64-bit build

[Jonathan M Davis]

Is the druntime posix.mak makefile not set up for a 64-bit build? I can't figure 
out how to make it build a 64-bit version, and it doesn't seem to have a lib32 
and lib64 directory or anything similar.

Looking at Phobos' posix.mak makefile, it looks like you build with MODEL=64, and 
it will do the 64-bit build and put the library in generated/linux/debug/64 
instead of generated/linux/debug/32 ( or generated/release/... for release). But 
if druntime isn't built as 64-bit, then I don't see as how you could build 
Phobos that way. druntime is obviously being built and run as 64-bit on the 
autotester, but I haven't a clue how.

What do I need to do to build druntime as 64-bit, and do the makefiles need 
updating?

- Jonathan M Davis