Revert "[Dexter] Remove builder from Dexter"

& Revert "[Dexter] Fix incorrect substitution errors in clang-cl builder"

This reverts commits 262520a3,
and 0b72b71c.

Failures occurred on two buildbots, the SIE buildbot:
https://lab.llvm.org/buildbot/#/builders/216/builds/26006

And the green dragon buildbot:
https://green.lab.llvm.org/green/view/LLDB/job/lldb-cmake/59091

Errors appear to be related to incorrect tool substitution in the Dexter
test commands, and a currently unknown error with one of the general
debuginfo tests that uses Dexter.