CI: Update to LLVM-12
The current stable release of LLVM is 12, update to that. While at it,
fix that we had not correctly upgraded to LLVM 11 previously.
Signed-off-by: 
Tom Rini <trini@konsulko.com>
The current stable release of LLVM is 12, update to that. While at it,
fix that we had not correctly upgraded to LLVM 11 previously.
Signed-off-by: Tom Rini <trini@konsulko.com>