C-- is no longer actively developed or widely used. The last significant update to the C-- project was in 2004. LLVM was one of the reasons why it declined. If you're looking for an alternative to LLVM, have a look at e.g. ECMA 335 CIL, WASM, QBE or ECS (see https://github.com/EigenCompilerSuite/), depending on your use-case.