Support for LLVM 9.0.0

PhASAR now supports LLVM 9. Checkout our development branch on Github ( Moving from LLVM 8 to LLVM 9 did not break any of PhASAR’s code. We only needed to make a small adjustment to the top-level CMakeLists.txt. Therefore, LLVM 8 is still supported and can be used without trouble: users need to adjust the find_package(LLVM [...] line of the top-level CMakeLists.txt. Have fun hacking on PhASAR!