Improved CMake integration of LLVM (#2103)

Added the paths for the CMake config files for LLVM 19 and higher to ``CMAKE_PREFIX_PATH``,
so that they will also be searched automatically.

Fix CI

Fix CI

Release 0.6.8

Fix of test (again)

Release candidate 0.6.6

Build 0.6.5 release. Fixed.

Updated for 0.6.4 release.

0.6.3 Release version.

Create release.