Revert workarounds expediting conversion of backend to D

[dlangBugzillaToGithub]

Mike Franklin reported this on 2018-05-20T02:21:03Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=18883

Description

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