d.godbolt.org now has modern gdc

[John Colvin]

For those who don't know, d.godbolt.org is an online 
compiler-disassembler for d, a sibling of http://gcc.godbolt.org/

For a long time it only had gdc 4.6.3, but it now has the latest 
binary release. Ldc may arrive as well, in time.

Thanks to Matt Godbolt who was very responsive and fast in 
updating it once I brought it to his attention.