Removal of gcc.config, std.c.unix modules, and x3 module generation from libphobos and libdruntime.

[Iain Buclaw]

Please take note for those who are using platforms not supported 
by druntime.

https://github.com/D-Programming-GDC/GDC/commit/ffed7d684e94d2b933a7d2f27403d8fb7de65314

Regards