Adding gdc to gcc

[Florian Weimer]

* Walter Bright:

> In other words, any changes in gdc that affect the front end should be
> given to Digital Mars, I will transfer the copyright to FSF, and get
> the license back. Otherwise, I cannot fold in those changes.

In this case, it might be simpler to contribute and maintain the
frontend under a less restrictive license, perhaps something
BSD-style.  (I'm assuming that the primary reason to choose the GPL
was compatibility with GCC, which might not be the case.)