This change does two things.
The first is to revert the llvm-clang-x86_64-sie-ubuntu-fast builder to the previous state, namely removing the build/test of LLDB. The LLDB project had a lot of test issues with the PS4 triple, and we decided we don't need it.
The second change is to break out the testing of the cross-project-tests to a separate builder that uses a native default triple (rather than the PS4 triple), builds the required projects, and then tests only the cross-project-tests suite. Our main goal here is to add some upstream coverage of the cross-project-tests suite, but since we are sharing a worker with the llvm-clang-x86_64-sie-ubuntu-fast job, we want it to run as quickly as possible