Change to use forked sources
    
    Since upstream does not target stable LLVM, it's a real hassle to
    maintain this package as-is. Fortunately, forking the source and
    backporting patches is pretty trivial.
    
    I setup a new fork:
    https://github.com/Mystro256/ROCm-Device-Libs/
    
    and I will be tagging using the LLVM major number + a patch number as I
    backport changes. E.g. 16.0 is the first tag that targets LLVM 16, while
    16.1 will have bugfix backports from newer ROCm releases.
    
    If you update LLVM, just change the bugfix_version to 0, as I prepare
    the intial *.0 tag as soon after the upstream LLVM release branch is
    created. E.g. I created 16.0 about a month ago.