dmd.dtoh: export genCppHdrFiles to C++

[ibuclaw]

Follow-up to #10801.

This allows genCppHdrFiles to be called from gdc.

[dlang-bot]

Thanks for your pull request, @ibuclaw!

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Testing this PR locally

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dub fetch digger
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[MoonlightSentinel]

Most of these changes are irrelevant to the C++ interface...

Also why move the ‚pragma once‘ After the comment?

[ibuclaw]

Most of these changes are irrelevant to the C++ interface...

Rationale of these three commits are:

1. FTBFS: dmd/mars.d doesn't exist in gdc source tree
2. FTBFS: Couldn't call genCppHdrFiles from C++
3. Allow for gdc to advertise itself as the generator.

Also why move the ‚pragma once‘ After the comment?

Usually (least in every other tool I've used and/or written) the generated file notice is on the first line. I found it surprising that it wasn't.

[MoonlightSentinel]

Rationale of these three commits are:

Thanks for the explanation. These changes seem reasonable but the PR title is a bit misleading.

Usually (least in every other tool I've used and/or written) the generated file notice is on the first line. I found it surprising that it wasn't.

Okay, improving user experience is always nice.