Comment # 1 on bug 1120098 from Aaron Puchert

My proposal would be to replace clang-*.0 by clang-*, since the minor version
should always be 0.
(http://blog.llvm.org/2016/12/llvms-new-versioning-scheme.html)

Further, I'd propose to abandon update-alternatives and directly use the
metapackage version, so /usr/bin/clang from package clang version 7 points to
/usr/bin/clang-7 directly. I don't think that update-alternatives provides any
benefits when the we actually choose the version via metapackage.