See "discussion": https://discourse.llvm.org/t/rfc-dexter-feature-removals/60462
With Dexter's inclusion in LLVM, test discovery and building is no longer required and is an active maintenance burden; this patch removes the builder and all associated features from Dexter. This does also mean removing the clang-opt-bisect feature; this is unfortunate collateral damage, as that tool does add functionality that is not otherwise available from a combination of Dexter and existing LLVM tools, but to my knowledge this tool has not seen much use in recent years and nobody yet has expressed a use-case for it. If it is in use, then it could either be reimplemented to take a build script as an argument (as with tools such as git-bisect and llvm-reduce), or implemented as a separate program with general support for "repeatedly run clang with opt-bisect-limit and run a script at each bisection" with a Dexter option.
For the most part this patch deletes builder-related folders completely, and removes other builder-related code from the rest of Dexter. No further functional changes are expected to appear in this patch. Tests have been updated to directly invoke clang (either with %clang or with %dexter_regression_test_build, which substitutes to clang++ -O0 -glldb or clang-cl /Zi /Od depending on platform) to build a temporary executable file and then run Dexter on that file.