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

[Michael Jones via llvm-commits]

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@@ -216,6 +216,27 @@ if (LIBC_TARGET_OS_IS_WINDOWS AND LLVM_LIBC_FULL_BUILD)
   message(FATAL_ERROR "Windows does not support full mode build.")
 endif ()
 
+if (LIBC_TARGET_OS_IS_LINUX)
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michaelrj-google wrote:

Would it make sense to automatically set `LLVM_LIBC_USE_HOST_KERNEL_HEADERS` for overlay builds?

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