Added rootfs overlay. Location is consistent with section 9.1 of buildroot manual.
Discovered 'make savedefconfig'.
Patch 1 of N: added menu option to enable D
Bumped GCC and binutils versions, because GDC 4.9 is (probably) significantly better than GDC 4.8
BUG FIX: GDC can't link against uClibc - changing to eglibc.
This increases the rootfs size from 22 MB to 30 MB.
BUG FIX: Github API requires the archive format to be specified
Patch 2 of N: Added code to download GDC and run the patch script