Add ImportC compiler to dmd

[Walter Bright]

On 5/13/2021 10:57 PM, Max Haughton wrote:
> The only other that I can say is that keep in mind that the blocker is using C 
> not compiling C. I don't want dmd to be my C compiler - so you only need to 
> understand GNU extensions that are used in header files (and don't appear in 
> inline functions in those headers, but still).

I know, it's just a bonus that it can be used as a standalone C compiler. It's 
not the point of ImportC. It does, however, make it much easier to test ImportC. 
And who knows what clever uses people will find for it! I'm always amazed at the 
things people do with D features.