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

Wed Jan 29 11:36:07 PST 2025

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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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nickdesaulniers wrote:

> The other issue is that for overlay mode we do actually need to look at the other libc's headers.

D'oh, you're right!

> My main concern is around default configurations.

This is something I hadn't even considered.  I can get behind wanting an optionless configure to build out of the box.  Let me think more about this over lunch.

> Currently, LLVM_LIBC_FULL_BUILD defaults to off, so overlay is the default. We should probably change that at some point, but that's a separate issue.

I agree. Filed #124973.

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