Add ImportC compiler to dmd

[Walter Bright]

On 5/10/2021 12:39 AM, Patrick Schluter wrote:
> The only thing that bothers me as it is now is the fact that it doesn't support 
> intializer list `{ intializers }`, which I suppose means that designated 
> initializers `{ .field = ..., [3]=... }`and compound statements `(type){ 
> initializers }` are not working either. This would be a real real problem for 
> modern C code (C99 and superior).

The only issue is { initializer-list } has no direct analog in D, so I've got to 
add one to the D side.

For the purpose of this prototype, I wished to avoid adding code that wasn't in 
cparse.d.