llvm9[1] is newly added to SLE15 SP2 and was arrived to Leap, we see duplicated
binaries issue between llvm9 and llvm7, see below,

i586:
  python3-clang:
  - llvm7
  - llvm9
x86_64:
  libc++-devel:
  - llvm7
  - llvm9
  libc++1:
  - llvm7
  - llvm9
  libc++abi-devel:
  - llvm7
  - llvm9
  libc++abi1:
  - llvm7
  - llvm9
  python3-clang:
  - llvm7
  - llvm9

llvm7 in SLE15 SP2 hasn't build but inherited from update channel thus this
isn't a problem there, however we need to find a solution for Leap.

Richard, seems it's not yet to have bugowner of llvm9 in SLE, I added you to
CC'ed due to llvm9 in SLE15 SP2 was submitted by you.

[1] https://build.opensuse.org/request/show/774578