Add ImportC compiler to dmd

[Walter Bright]

On 5/11/2021 6:37 AM, jmh530 wrote:
> Am I right that Walter basically just moved the warp codebase from the Facebook 
> archive to the Digital Mars one and renamed it dmpp (with maybe some tweaks)?

Not exactly. It was developed in parallel with the Warp repository, for the 
simple reason that I did not have push rights on Facebook repositories. There 
are likely some small differences, but I don't know what they are.

Note that it's Boost licensed, so this is not a problem.

Should probably put dmpp on dub.