[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]

================
@@ -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",
----------------
lntue wrote:

Yes, I plan to get rid of `LIBC_ERRNO_MODE_SYSTEM` or just pointing that to `LIBC_ERRNO_MODE_INLINE` eventually.

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