MinGW-w64 runtime library inclusion (Clang-compiled) for proper Win64 support?

[kink]

> In the case of reals, simple things should work, but DMD packs 
> together 80-bit reals end-to-end (i.e. 10 byte spacing), 
> whereas LLVM chooses 12 byte alignment.

For 32-bit LLVM targets that is; sizeof(long double) == 16 bytes 
for the Win64 targets, so that the required 8-bytes alignment can 
be enforced.