This new release now includes the IEEE VHDL libraries, so we don't
need to download and copy them around by hand. The patches to use
newer LLVM versions are not needed anymore. Lastly, now we pass a
few --enable-foo and --with-bar options to the configure script to
enable additional features.
Allow building Nvc against LLVM 7. The llvm6 and llvm6-libs packages are
not available anymore, but picking a coupld of commits (which are not
included in any release) from the repository makes things
