Bug 18363 – we should autogenerate duplicate “.h” header files in dmd to keep them in sync

eg src/dmd/init.d vs src/dmd/init.h * dtoh was reverted (https://github.com/dlang/tools/pull/125) related: https://issues.dlang.org/show_bug.cgi?id=9285 Issue 9285 - dtoh utility - convert D files to C++ header files (but that was not specific to header files in dmd sources) * https://github.com/dlang/dmd/pull/5082 [WIP] Generate C++ header files from public extern (C++) declarations that was started on sept 2015

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