There is a frontend for the D language based on GCC, called gdc.
It has been accepted for inclusion in GCC, but it would be nice to have the language supported before that inclusion work is completed (and the next subsequent GCC major release occurs) .

I've attached my patched Funtoo gcc ebuild for gcc 5.4.0, which is loosely based on the Gentoo version provided by the dlang overlay.

GDC has dedicated git branches (gdc-{4.7,4.8,4.9,5,6,7}) to patch official GCC releases, while the master branch follows latest GCC upstream development.