Comment # 1 on bug 1145444 from Aaron Puchert

The scan-* recommendations of clang8 are unversioned, so they are satisfied by
older versions of clang as well:

$ rpm -q --recommends clang8
clang8-checker
scan-build
scan-view

"Provides" of clang8-checker are unversioned as well, so zypper just chooses
one:

% rpm -q --provides clang9-checker
clang8-checker = 8.0.1-...
clang8-checker(x86-64) = 8.0.1-...
scan-build
scan-view

One obvious fix would be to remove the scan-* recommendations from clang, since
they are provided by clang-checker, which we also recommend.

Perhaps I'll also version the "Provides" in the future, so that newer versions
have priority.