swift234

Clean up uses of swift-compiler-verison and clang_repository_string

Bring this build setting in line with swift-compiler-version:

- Use "clang-compiler-version" instead of "repository_string"
- Don't append the clang compiler version to the swift one.
- Clean up uses in build-script-impl and build-presets.ini.
- Clean up uses in CMake

Swift SVN r32794