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

[Alexey Samsonov via llvm-commits]

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@@ -46,4 +46,7 @@ LIBC_CONFIGURE_OPTIONS = [
 
     # Documentation in libc/src/__support/libc_assert.h
     # "LIBC_COPT_USE_C_ASSERT",
+
+    # Use system errno.
+    "LIBC_ERRNO_MODE=LIBC_ERRNO_MODE_SYSTEM",
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vonosmas wrote:

What is the eventual plan for `LIBC_ERRNO_MODE_SYSTEM`? I understand you're adding the new mode now to meet the goals of exposing some of the errno-using code through `libc/shared/`, but do you plan to eventually get rid of `LIBC_ERRNO_MODE_SYSTEM` mode altogether, since the code in the overlay public-packaging mode may be switched to an inline version as well?

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