Bug 18883 – Revert workarounds expediting conversion of backend to D

At the time the following PRs were created, the host compiler 2.068.2 (I believe). It had mangling issues that prevented conversion of the DMD backend to D. Therefore, Walter, insisted on a number of workarounds to expedite conversion of the backed to D without having to wait for an updated host compiler. These workarounds should eventually be reverted (at least those that still remain after the conversion). https://github.com/dlang/dmd/pull/7416 -- See also https://github.com/dlang/dmd/pull/7505 https://github.com/dlang/dmd/pull/7523 https://github.com/dlang/dmd/pull/8249

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