The patch [1] that introduces support for KFreeBSD includes a silly rename of an enum value from "KFreeBSD" to "kFreeBSD" and breaks the LLVM API for no reason at all.
I'd suggest to revert those renamings. [1] https://salsa.debian.org/pkg-llvm-team/llvm-toolchain/commit/de8350eea4269a1548bf4d73bc640d6e516841ce
