[libc] [llvm] [libc] Move libc_errno.h to libc/src/__support and make LIBC_ERRNO_MODE_SYSTEM to be header-only. (PR #143187)

[via llvm-commits]

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@@ -9,6 +9,7 @@
 #ifndef LLVM_LIBC_SHARED_FP_BITS_H
 #define LLVM_LIBC_SHARED_FP_BITS_H
 
+#include "libc_common.h"
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lntue wrote:

The other are GPU RPC headers.  I'll let @jhuber6 decide whether he wants them to be included or not.  Since those do not use `LIBC_NAMESPACE` macro at all.

https://github.com/llvm/llvm-project/pull/143187