GDC and GCC. Merging 4.9 but cannot understand something

[Larry]

Hello,

I read somewhere that gcd and gcc will be merged:
http://forum.dlang.org/thread/kyoredrrscclqziyaesp@forum.dlang.org?page=1

But I cannot understand how different languages can use the same 
compiler.

D is not far from c/c++ but it has its own hacks, right ?

Are gdc devs developping D as close as c/c++ as possible ?

I cannot understand how it will work.

If someone could enlighten me on the logical and what to expect, 
please, tell me.

Many thanks,

See you,

Larry