Add ImportC support via `dmd -H`.

[jnms-me]

This adds .c, .h and .i files (see https://dlang.org/spec/importc.html) as 'alternative' (lower priority) importable files. $DMD or dmd is called on the source file with -H to produce a .di file, which we can parse as normal. Note that .h files are only supported by current dmd master, since the merge of https://github.com/dlang/dmd/pull/21692.

[github-actions[bot]]

Thanks for your Pull Request and making D better!

This comment will automatically be updated to summarize some statistics in a few minutes.

[jnms-me]

See https://github.com/Pure-D/serve-d/issues/328.

[jnms-me]

Module auto-complete in serve-d doesn't seem to work yet. Any idea where that would be implemented?

[WebFreak001]

you mean auto complete for this:

import some.mod|;

?

[jnms-me]

Yes, that doesn't show ImportC modules yet.