[libc] [llvm] [libc][cmake][linux] require new LLVM_LIBC_USE_HOST_KERNEL_HEADERS or LIBC_KERNEL_HEADERS (PR #123820)

[Nick Desaulniers via llvm-commits]

nickdesaulniers wrote:

> presubmit test failures

probably need to update .github/workflows/libc-overlay-tests.yml, too.

https://github.com/llvm/llvm-project/pull/123820